diff --git a/src/core/mcp/include/sourcemeta/core/mcp_capabilities.h b/src/core/mcp/include/sourcemeta/core/mcp_capabilities.h
index 9c317bc8b..2e79054a0 100644
--- a/src/core/mcp/include/sourcemeta/core/mcp_capabilities.h
+++ b/src/core/mcp/include/sourcemeta/core/mcp_capabilities.h
@@ -168,9 +168,9 @@ struct MCPServerCapabilities {
 ///
 /// @see
 /// https://modelcontextprotocol.io/specification/2026-07-28/schema#clientcapabilities
-SOURCEMETA_CORE_MCP_EXPORT
-auto mcp_parse_client_capabilities(const MCPProtocolVersion version,
-                                   const sourcemeta::core::JSON &capabilities)
+[[nodiscard]] SOURCEMETA_CORE_MCP_EXPORT auto
+mcp_parse_client_capabilities(const MCPProtocolVersion version,
+                              const sourcemeta::core::JSON &capabilities)
     -> MCPClientCapabilities;
 
 /// @ingroup mcp
@@ -199,9 +199,9 @@ auto mcp_parse_client_capabilities(const MCPProtocolVersion version,
 ///
 /// @see
 /// https://modelcontextprotocol.io/specification/2026-07-28/schema#clientcapabilities
-SOURCEMETA_CORE_MCP_EXPORT
-auto mcp_serialize_client_capabilities(
-    const MCPProtocolVersion version, const MCPClientCapabilities &capabilities)
+[[nodiscard]] SOURCEMETA_CORE_MCP_EXPORT auto
+mcp_serialize_client_capabilities(const MCPProtocolVersion version,
+                                  const MCPClientCapabilities &capabilities)
     -> sourcemeta::core::JSON;
 
 /// @ingroup mcp
@@ -226,9 +226,9 @@ auto mcp_serialize_client_capabilities(
 ///
 /// @see
 /// https://modelcontextprotocol.io/specification/2026-07-28/schema#servercapabilities
-SOURCEMETA_CORE_MCP_EXPORT
-auto mcp_parse_server_capabilities(MCPProtocolVersion version,
-                                   const JSON &capabilities)
+[[nodiscard]] SOURCEMETA_CORE_MCP_EXPORT auto
+mcp_parse_server_capabilities(MCPProtocolVersion version,
+                              const JSON &capabilities)
     -> MCPServerCapabilities;
 
 /// @ingroup mcp
@@ -252,9 +252,9 @@ auto mcp_parse_server_capabilities(MCPProtocolVersion version,
 ///
 /// @see
 /// https://modelcontextprotocol.io/specification/2026-07-28/schema#servercapabilities
-SOURCEMETA_CORE_MCP_EXPORT
-auto mcp_serialize_server_capabilities(
-    MCPProtocolVersion version, const MCPServerCapabilities &capabilities)
+[[nodiscard]] SOURCEMETA_CORE_MCP_EXPORT auto
+mcp_serialize_server_capabilities(MCPProtocolVersion version,
+                                  const MCPServerCapabilities &capabilities)
     -> JSON;
 
 } // namespace sourcemeta::core
diff --git a/src/core/mcp/include/sourcemeta/core/mcp_error.h b/src/core/mcp/include/sourcemeta/core/mcp_error.h
index f5333f52f..1878f878c 100644
--- a/src/core/mcp/include/sourcemeta/core/mcp_error.h
+++ b/src/core/mcp/include/sourcemeta/core/mcp_error.h
@@ -109,11 +109,11 @@ enum class MCPErrorContext : std::uint8_t {
 ///
 /// @see
 /// https://modelcontextprotocol.io/specification/2026-07-28/basic/index#responses
-SOURCEMETA_CORE_MCP_EXPORT
-auto mcp_make_error(MCPProtocolVersion version, const JSON *identifier,
-                    std::int64_t code, JSON::StringView message,
-                    std::optional<JSON> data = std::nullopt,
-                    MCPErrorContext context = MCPErrorContext::Request) -> JSON;
+[[nodiscard]] SOURCEMETA_CORE_MCP_EXPORT auto
+mcp_make_error(MCPProtocolVersion version, const JSON *identifier,
+               std::int64_t code, JSON::StringView message,
+               std::optional<JSON> data = std::nullopt,
+               MCPErrorContext context = MCPErrorContext::Request) -> JSON;
 
 /// @ingroup mcp
 /// The legacy MCP error code returned when a requested resource cannot be
@@ -196,8 +196,9 @@ constexpr std::int64_t MCP_CODE_UNSUPPORTED_PROTOCOL_VERSION{-32022};
 /// @see
 /// https://modelcontextprotocol.io/specification/2026-07-28/basic/transports/streamable-http#server-validation
 /// https://modelcontextprotocol.io/specification/2026-07-28/basic/index#_meta
-constexpr auto mcp_error_code_to_http_status(const MCPProtocolVersion version,
-                                             const std::int64_t code) noexcept
+[[nodiscard]] constexpr auto
+mcp_error_code_to_http_status(const MCPProtocolVersion version,
+                              const std::int64_t code) noexcept
     -> std::optional<HTTPStatus> {
   if (version != MCPProtocolVersion::V_2026_07_28) {
     return std::nullopt;
@@ -247,8 +248,8 @@ constexpr auto mcp_error_code_to_http_status(const MCPProtocolVersion version,
 ///
 /// @see
 /// https://modelcontextprotocol.io/specification/2026-07-28/basic/index#error-codes
-SOURCEMETA_CORE_MCP_EXPORT
-auto mcp_make_error_unsupported_protocol_version(
+[[nodiscard]] SOURCEMETA_CORE_MCP_EXPORT auto
+mcp_make_error_unsupported_protocol_version(
     const MCPProtocolVersion version, const sourcemeta::core::JSON *identifier,
     const JSON::StringView requested,
     const std::span<const JSON::StringView> supported)
@@ -282,8 +283,8 @@ auto mcp_make_error_unsupported_protocol_version(
 ///
 /// @see
 /// https://modelcontextprotocol.io/specification/2026-07-28/basic/index#error-codes
-SOURCEMETA_CORE_MCP_EXPORT
-auto mcp_make_error_missing_required_capability(
+[[nodiscard]] SOURCEMETA_CORE_MCP_EXPORT auto
+mcp_make_error_missing_required_capability(
     const MCPProtocolVersion version, const sourcemeta::core::JSON *identifier,
     sourcemeta::core::JSON required_capabilities,
     const JSON::StringView message) -> sourcemeta::core::JSON;
@@ -310,11 +311,9 @@ auto mcp_make_error_missing_required_capability(
 ///
 /// @see
 /// https://modelcontextprotocol.io/specification/2026-07-28/basic/transports/streamable-http#schema-extension
-SOURCEMETA_CORE_MCP_EXPORT
-auto mcp_make_error_header_mismatch(const MCPProtocolVersion version,
-                                    const sourcemeta::core::JSON *identifier,
-                                    const JSON::StringView message)
-    -> sourcemeta::core::JSON;
+[[nodiscard]] SOURCEMETA_CORE_MCP_EXPORT auto mcp_make_error_header_mismatch(
+    const MCPProtocolVersion version, const sourcemeta::core::JSON *identifier,
+    const JSON::StringView message) -> sourcemeta::core::JSON;
 
 /// @ingroup mcp
 /// Build a JSON-RPC error response for header mismatch (-32020) with detailed
@@ -346,13 +345,10 @@ auto mcp_make_error_header_mismatch(const MCPProtocolVersion version,
 ///
 /// @see
 /// https://modelcontextprotocol.io/specification/2026-07-28/basic/transports/streamable-http#schema-extension
-SOURCEMETA_CORE_MCP_EXPORT
-auto mcp_make_error_header_mismatch(const MCPProtocolVersion version,
-                                    const sourcemeta::core::JSON *identifier,
-                                    const JSON::StringView header_name,
-                                    const JSON::StringView header_value,
-                                    const JSON::StringView body_value)
-    -> sourcemeta::core::JSON;
+[[nodiscard]] SOURCEMETA_CORE_MCP_EXPORT auto mcp_make_error_header_mismatch(
+    const MCPProtocolVersion version, const sourcemeta::core::JSON *identifier,
+    const JSON::StringView header_name, const JSON::StringView header_value,
+    const JSON::StringView body_value) -> sourcemeta::core::JSON;
 
 /// @ingroup mcp
 /// Build a JSON-RPC error response for header mismatch (-32020) reporting an
@@ -379,11 +375,9 @@ auto mcp_make_error_header_mismatch(const MCPProtocolVersion version,
 ///
 /// @see
 /// https://modelcontextprotocol.io/specification/2026-07-28/basic/transports/streamable-http#schema-extension
-SOURCEMETA_CORE_MCP_EXPORT
-auto mcp_make_error_header_mismatch(const MCPProtocolVersion version,
-                                    const sourcemeta::core::JSON *identifier,
-                                    const JSON::StringView header_name,
-                                    const JSON::StringView header_value)
+[[nodiscard]] SOURCEMETA_CORE_MCP_EXPORT auto mcp_make_error_header_mismatch(
+    const MCPProtocolVersion version, const sourcemeta::core::JSON *identifier,
+    const JSON::StringView header_name, const JSON::StringView header_value)
     -> sourcemeta::core::JSON;
 
 /// @ingroup mcp
@@ -414,9 +408,9 @@ auto mcp_make_error_header_mismatch(const MCPProtocolVersion version,
 ///
 /// @see
 /// https://modelcontextprotocol.io/specification/2026-07-28/server/resources#error-handling
-SOURCEMETA_CORE_MCP_EXPORT
-auto mcp_make_error_resource_not_found(const MCPProtocolVersion version,
-                                       const sourcemeta::core::JSON *identifier)
+[[nodiscard]] SOURCEMETA_CORE_MCP_EXPORT auto
+mcp_make_error_resource_not_found(const MCPProtocolVersion version,
+                                  const sourcemeta::core::JSON *identifier)
     -> sourcemeta::core::JSON;
 
 } // namespace sourcemeta::core
diff --git a/src/core/mcp/include/sourcemeta/core/mcp_headers.h b/src/core/mcp/include/sourcemeta/core/mcp_headers.h
index a10fdb6db..54993d054 100644
--- a/src/core/mcp/include/sourcemeta/core/mcp_headers.h
+++ b/src/core/mcp/include/sourcemeta/core/mcp_headers.h
@@ -141,8 +141,8 @@ struct MCPRequestMeta {
 ///
 /// @see
 /// https://modelcontextprotocol.io/specification/2026-07-28/basic/index#_meta
-SOURCEMETA_CORE_MCP_EXPORT
-auto mcp_validate_request_meta(const sourcemeta::core::JSON &envelope)
+[[nodiscard]] SOURCEMETA_CORE_MCP_EXPORT auto
+mcp_validate_request_meta(const sourcemeta::core::JSON &envelope)
     -> std::pair<MCPRequestMetaStatus, std::optional<MCPRequestMeta>>;
 
 /// @ingroup mcp
@@ -166,8 +166,8 @@ auto mcp_validate_request_meta(const sourcemeta::core::JSON &envelope)
 ///
 /// @see
 /// https://modelcontextprotocol.io/specification/2026-07-28/basic/index#_meta
-SOURCEMETA_CORE_MCP_EXPORT
-auto mcp_validate_request_parameters(const JSON &parameters)
+[[nodiscard]] SOURCEMETA_CORE_MCP_EXPORT auto
+mcp_validate_request_parameters(const JSON &parameters)
     -> std::pair<MCPRequestMetaStatus, std::optional<MCPRequestMeta>>;
 
 /// @ingroup mcp
@@ -216,8 +216,7 @@ auto mcp_validate_request_parameters(const JSON &parameters)
 ///
 /// @see
 /// https://modelcontextprotocol.io/specification/2026-07-28/basic/index#error-codes
-SOURCEMETA_CORE_MCP_EXPORT
-auto mcp_make_error_request_meta(
+[[nodiscard]] SOURCEMETA_CORE_MCP_EXPORT auto mcp_make_error_request_meta(
     const MCPProtocolVersion version, const sourcemeta::core::JSON *identifier,
     const MCPRequestMetaStatus status, const JSON::StringView requested,
     const std::span<const JSON::StringView> supported)
@@ -242,8 +241,8 @@ auto mcp_make_error_request_meta(
 ///
 /// @see
 /// https://modelcontextprotocol.io/specification/2026-07-28/basic/transports/streamable-http#standard-request-headers
-SOURCEMETA_CORE_MCP_EXPORT
-auto mcp_request_name_from_body(const sourcemeta::core::JSON &envelope)
+[[nodiscard]] SOURCEMETA_CORE_MCP_EXPORT auto
+mcp_request_name_from_body(const sourcemeta::core::JSON &envelope)
     -> std::optional<JSON::StringView>;
 
 /// @ingroup mcp
@@ -285,8 +284,7 @@ auto mcp_request_name_from_body(const sourcemeta::core::JSON &envelope)
 ///
 /// @see
 /// https://modelcontextprotocol.io/specification/2026-07-28/basic/transports/streamable-http#server-validation
-SOURCEMETA_CORE_MCP_EXPORT
-auto mcp_validate_request_headers(
+[[nodiscard]] SOURCEMETA_CORE_MCP_EXPORT auto mcp_validate_request_headers(
     const MCPProtocolVersion version,
     const std::optional<JSON::StringView> &protocol_version_header,
     const std::optional<JSON::StringView> &method_header,
@@ -316,8 +314,8 @@ auto mcp_validate_request_headers(
 ///
 /// @see
 /// https://modelcontextprotocol.io/specification/2026-07-28/basic/transports/streamable-http#value-encoding
-SOURCEMETA_CORE_MCP_EXPORT
-auto mcp_encode_header_value(JSON::StringView value) -> std::string;
+[[nodiscard]] SOURCEMETA_CORE_MCP_EXPORT auto
+mcp_encode_header_value(JSON::StringView value) -> std::string;
 
 /// @ingroup mcp
 /// Validate a borrowed HTTP header collection. Names are case insensitive.
@@ -363,8 +361,7 @@ auto mcp_encode_header_value(JSON::StringView value) -> std::string;
 ///
 /// @see
 /// https://modelcontextprotocol.io/specification/2026-07-28/basic/transports/streamable-http#server-validation
-SOURCEMETA_CORE_MCP_EXPORT
-auto mcp_validate_request_headers(
+[[nodiscard]] SOURCEMETA_CORE_MCP_EXPORT auto mcp_validate_request_headers(
     MCPProtocolVersion version,
     std::span<const std::pair<JSON::StringView, JSON::StringView>> headers,
     const JSON &envelope, std::span<const JSON::StringView> supported_versions)
@@ -442,9 +439,9 @@ struct MCPHeaderParameter {
 ///
 /// @see
 /// https://modelcontextprotocol.io/specification/2026-07-28/basic/transports/streamable-http#schema-extension
-SOURCEMETA_CORE_MCP_EXPORT
-auto mcp_make_parameter_headers(std::span<const MCPHeaderParameter> parameters,
-                                const JSON &arguments)
+[[nodiscard]] SOURCEMETA_CORE_MCP_EXPORT auto
+mcp_make_parameter_headers(std::span<const MCPHeaderParameter> parameters,
+                           const JSON &arguments)
     -> std::vector<std::pair<std::string, std::string>>;
 
 /// @ingroup mcp
@@ -478,8 +475,7 @@ auto mcp_make_parameter_headers(std::span<const MCPHeaderParameter> parameters,
 ///
 /// @see
 /// https://modelcontextprotocol.io/specification/2026-07-28/basic/transports/streamable-http#server-validation
-SOURCEMETA_CORE_MCP_EXPORT
-auto mcp_validate_parameter_headers(
+[[nodiscard]] SOURCEMETA_CORE_MCP_EXPORT auto mcp_validate_parameter_headers(
     MCPProtocolVersion version, const JSON &identifier,
     std::span<const MCPHeaderParameter> parameters, const JSON &arguments,
     std::span<const std::pair<JSON::StringView, JSON::StringView>> headers)
diff --git a/src/core/mcp/include/sourcemeta/core/mcp_logging.h b/src/core/mcp/include/sourcemeta/core/mcp_logging.h
index 707dc2b63..9c7b5e696 100644
--- a/src/core/mcp/include/sourcemeta/core/mcp_logging.h
+++ b/src/core/mcp/include/sourcemeta/core/mcp_logging.h
@@ -55,8 +55,8 @@ enum class MCPLogLevel : std::uint8_t {
 ///
 /// @see
 /// https://modelcontextprotocol.io/specification/2026-07-28/server/utilities/logging
-constexpr auto mcp_log_level_string(const MCPLogLevel level) noexcept
-    -> JSON::StringView {
+[[nodiscard]] constexpr auto
+mcp_log_level_string(const MCPLogLevel level) noexcept -> JSON::StringView {
   switch (level) {
     case MCPLogLevel::Debug:
       return "debug";
@@ -99,7 +99,8 @@ constexpr auto mcp_log_level_string(const MCPLogLevel level) noexcept
 ///
 /// @see
 /// https://modelcontextprotocol.io/specification/2026-07-28/server/utilities/logging
-constexpr auto mcp_resolve_log_level(const JSON::StringView value) noexcept
+[[nodiscard]] constexpr auto
+mcp_resolve_log_level(const JSON::StringView value) noexcept
     -> std::optional<MCPLogLevel> {
   constexpr std::array<MCPLogLevel, 8> LEVELS{
       {MCPLogLevel::Debug, MCPLogLevel::Info, MCPLogLevel::Notice,
@@ -135,9 +136,9 @@ constexpr auto mcp_resolve_log_level(const JSON::StringView value) noexcept
 ///
 /// @see
 /// https://modelcontextprotocol.io/specification/2026-07-28/server/utilities/logging
-constexpr auto mcp_log_level_enabled(const MCPLogLevel level,
-                                     const MCPLogLevel threshold) noexcept
-    -> bool {
+[[nodiscard]] constexpr auto
+mcp_log_level_enabled(const MCPLogLevel level,
+                      const MCPLogLevel threshold) noexcept -> bool {
   return level >= threshold;
 }
 
diff --git a/src/core/mcp/include/sourcemeta/core/mcp_protocol.h b/src/core/mcp/include/sourcemeta/core/mcp_protocol.h
index def5acdd9..0b4260cea 100644
--- a/src/core/mcp/include/sourcemeta/core/mcp_protocol.h
+++ b/src/core/mcp/include/sourcemeta/core/mcp_protocol.h
@@ -384,7 +384,7 @@ constexpr JSON::StringView MCP_METHOD_TASKS_RESULT{"tasks/result"};
 ///
 /// @see
 /// https://modelcontextprotocol.io/specification/2026-07-28/basic/versioning
-constexpr auto
+[[nodiscard]] constexpr auto
 mcp_protocol_version_string(const MCPProtocolVersion version) noexcept
     -> JSON::StringView {
   switch (version) {
@@ -421,7 +421,7 @@ mcp_protocol_version_string(const MCPProtocolVersion version) noexcept
 ///
 /// @see
 /// https://modelcontextprotocol.io/specification/2026-07-28/basic/versioning
-constexpr auto
+[[nodiscard]] constexpr auto
 mcp_resolve_protocol_version(const JSON::StringView value) noexcept
     -> std::optional<MCPProtocolVersion> {
   if (value == MCP_PROTOCOL_VERSION_2026_07_28) {
@@ -458,7 +458,7 @@ mcp_resolve_protocol_version(const JSON::StringView value) noexcept
 ///
 /// @see
 /// https://modelcontextprotocol.io/specification/2026-07-28/basic/versioning
-constexpr auto
+[[nodiscard]] constexpr auto
 mcp_protocol_version_at_least(const MCPProtocolVersion current,
                               const MCPProtocolVersion minimum) noexcept
     -> bool {
@@ -480,7 +480,7 @@ mcp_protocol_version_at_least(const MCPProtocolVersion current,
 ///
 /// @see
 /// https://modelcontextprotocol.io/specification/2026-07-28/basic/versioning
-constexpr auto
+[[nodiscard]] constexpr auto
 mcp_protocol_version_is_valid(const JSON::StringView value) noexcept -> bool {
   return mcp_resolve_protocol_version(value).has_value();
 }
@@ -502,7 +502,7 @@ mcp_protocol_version_is_valid(const JSON::StringView value) noexcept -> bool {
 ///
 /// @see
 /// https://modelcontextprotocol.io/specification/2026-07-28/basic/lifecycle
-constexpr auto
+[[nodiscard]] constexpr auto
 mcp_uses_initialization_handshake(const MCPProtocolVersion version) noexcept
     -> bool {
   return version != MCPProtocolVersion::V_2026_07_28;
@@ -524,8 +524,8 @@ mcp_uses_initialization_handshake(const MCPProtocolVersion version) noexcept
 ///
 /// @see
 /// https://modelcontextprotocol.io/specification/2026-07-28/basic/lifecycle
-constexpr auto mcp_supports_ping(const MCPProtocolVersion version) noexcept
-    -> bool {
+[[nodiscard]] constexpr auto
+mcp_supports_ping(const MCPProtocolVersion version) noexcept -> bool {
   return version != MCPProtocolVersion::V_2026_07_28;
 }
 
@@ -546,7 +546,7 @@ constexpr auto mcp_supports_ping(const MCPProtocolVersion version) noexcept
 ///
 /// @see
 /// https://modelcontextprotocol.io/specification/2026-07-28/basic/index#_meta
-constexpr auto
+[[nodiscard]] constexpr auto
 mcp_requires_request_meta(const MCPProtocolVersion version) noexcept -> bool {
   return version == MCPProtocolVersion::V_2026_07_28;
 }
@@ -568,7 +568,7 @@ mcp_requires_request_meta(const MCPProtocolVersion version) noexcept -> bool {
 ///
 /// @see
 /// https://modelcontextprotocol.io/specification/2026-07-28/schema
-constexpr auto
+[[nodiscard]] constexpr auto
 mcp_requires_result_type(const MCPProtocolVersion version) noexcept -> bool {
   return version == MCPProtocolVersion::V_2026_07_28;
 }
@@ -590,7 +590,7 @@ mcp_requires_result_type(const MCPProtocolVersion version) noexcept -> bool {
 ///
 /// @see
 /// https://modelcontextprotocol.io/specification/2026-07-28/server/utilities/caching#cacheable-results
-constexpr auto
+[[nodiscard]] constexpr auto
 mcp_requires_cacheable_metadata(const MCPProtocolVersion version) noexcept
     -> bool {
   return version == MCPProtocolVersion::V_2026_07_28;
@@ -613,7 +613,7 @@ mcp_requires_cacheable_metadata(const MCPProtocolVersion version) noexcept
 ///
 /// @see
 /// https://modelcontextprotocol.io/specification/2026-07-28/server/discover
-constexpr auto
+[[nodiscard]] constexpr auto
 mcp_supports_server_discover(const MCPProtocolVersion version) noexcept
     -> bool {
   return version == MCPProtocolVersion::V_2026_07_28;
@@ -636,7 +636,7 @@ mcp_supports_server_discover(const MCPProtocolVersion version) noexcept
 ///
 /// @see
 /// https://modelcontextprotocol.io/specification/2026-07-28/basic/patterns/subscriptions
-constexpr auto
+[[nodiscard]] constexpr auto
 mcp_supports_subscriptions_listen(const MCPProtocolVersion version) noexcept
     -> bool {
   return version == MCPProtocolVersion::V_2026_07_28;
@@ -659,8 +659,8 @@ mcp_supports_subscriptions_listen(const MCPProtocolVersion version) noexcept
 ///
 /// @see
 /// https://modelcontextprotocol.io/specification/2026-07-28/basic/patterns/mrtr
-constexpr auto mcp_supports_mrtr(const MCPProtocolVersion version) noexcept
-    -> bool {
+[[nodiscard]] constexpr auto
+mcp_supports_mrtr(const MCPProtocolVersion version) noexcept -> bool {
   return version == MCPProtocolVersion::V_2026_07_28;
 }
 
@@ -681,7 +681,7 @@ constexpr auto mcp_supports_mrtr(const MCPProtocolVersion version) noexcept
 ///
 /// @see
 /// https://modelcontextprotocol.io/specification/2026-07-28/basic/transports/streamable-http
-constexpr auto
+[[nodiscard]] constexpr auto
 mcp_supports_protocol_sessions(const MCPProtocolVersion version) noexcept
     -> bool {
   return version != MCPProtocolVersion::V_2026_07_28;
@@ -704,7 +704,7 @@ mcp_supports_protocol_sessions(const MCPProtocolVersion version) noexcept
 ///
 /// @see
 /// https://modelcontextprotocol.io/specification/2026-07-28/server/tools
-constexpr auto
+[[nodiscard]] constexpr auto
 mcp_supports_output_schema(const MCPProtocolVersion version) noexcept -> bool {
   return mcp_protocol_version_at_least(version,
                                        MCPProtocolVersion::V_2025_06_18);
@@ -726,7 +726,7 @@ mcp_supports_output_schema(const MCPProtocolVersion version) noexcept -> bool {
 ///
 /// @see
 /// https://modelcontextprotocol.io/specification/2026-07-28/server/tools
-constexpr auto
+[[nodiscard]] constexpr auto
 mcp_supports_structured_content(const MCPProtocolVersion version) noexcept
     -> bool {
   return mcp_protocol_version_at_least(version,
@@ -749,7 +749,7 @@ mcp_supports_structured_content(const MCPProtocolVersion version) noexcept
 ///
 /// @see
 /// https://modelcontextprotocol.io/specification/2026-07-28/schema
-constexpr auto
+[[nodiscard]] constexpr auto
 mcp_supports_resource_link_content(const MCPProtocolVersion version) noexcept
     -> bool {
   return mcp_protocol_version_at_least(version,
@@ -772,7 +772,7 @@ mcp_supports_resource_link_content(const MCPProtocolVersion version) noexcept
 ///
 /// @see
 /// https://modelcontextprotocol.io/specification/2026-07-28/schema
-constexpr auto
+[[nodiscard]] constexpr auto
 mcp_supports_implementation_title(const MCPProtocolVersion version) noexcept
     -> bool {
   return mcp_protocol_version_at_least(version,
@@ -796,7 +796,7 @@ mcp_supports_implementation_title(const MCPProtocolVersion version) noexcept
 ///
 /// @see
 /// https://modelcontextprotocol.io/specification/2026-07-28/schema
-constexpr auto mcp_supports_implementation_description(
+[[nodiscard]] constexpr auto mcp_supports_implementation_description(
     const MCPProtocolVersion version) noexcept -> bool {
   return mcp_protocol_version_at_least(version,
                                        MCPProtocolVersion::V_2025_11_25);
@@ -819,7 +819,7 @@ constexpr auto mcp_supports_implementation_description(
 ///
 /// @see
 /// https://modelcontextprotocol.io/specification/2026-07-28/schema
-constexpr auto mcp_supports_implementation_website_url(
+[[nodiscard]] constexpr auto mcp_supports_implementation_website_url(
     const MCPProtocolVersion version) noexcept -> bool {
   return mcp_protocol_version_at_least(version,
                                        MCPProtocolVersion::V_2025_11_25);
@@ -841,7 +841,7 @@ constexpr auto mcp_supports_implementation_website_url(
 ///
 /// @see
 /// https://modelcontextprotocol.io/specification/2026-07-28/basic/transports/streamable-http
-constexpr auto
+[[nodiscard]] constexpr auto
 mcp_supports_jsonrpc_batching(const MCPProtocolVersion version) noexcept
     -> bool {
   return version == MCPProtocolVersion::V_2025_03_26;
@@ -863,9 +863,9 @@ mcp_supports_jsonrpc_batching(const MCPProtocolVersion version) noexcept
 ///
 /// @see
 /// https://modelcontextprotocol.io/specification/2026-07-28/schema
-constexpr auto mcp_is_request_method(const MCPProtocolVersion version,
-                                     const JSON::StringView method) noexcept
-    -> bool {
+[[nodiscard]] constexpr auto
+mcp_is_request_method(const MCPProtocolVersion version,
+                      const JSON::StringView method) noexcept -> bool {
   switch (version) {
     case MCPProtocolVersion::V_2025_03_26:
     case MCPProtocolVersion::V_2025_06_18:
@@ -931,7 +931,7 @@ constexpr auto mcp_is_request_method(const MCPProtocolVersion version,
 ///
 /// @see
 /// https://modelcontextprotocol.io/specification/2026-07-28/schema
-constexpr auto
+[[nodiscard]] constexpr auto
 mcp_is_server_request_method(const MCPProtocolVersion version,
                              const JSON::StringView method) noexcept -> bool {
   switch (version) {
@@ -978,7 +978,7 @@ mcp_is_server_request_method(const MCPProtocolVersion version,
 ///
 /// @see
 /// https://modelcontextprotocol.io/specification/2026-07-28/schema
-constexpr auto
+[[nodiscard]] constexpr auto
 mcp_is_notification_method(const MCPProtocolVersion version,
                            const JSON::StringView method) noexcept -> bool {
   switch (version) {
@@ -1040,7 +1040,7 @@ mcp_is_notification_method(const MCPProtocolVersion version,
 ///
 /// @see
 /// https://modelcontextprotocol.io/specification/2026-07-28/basic/patterns/mrtr
-constexpr auto
+[[nodiscard]] constexpr auto
 mcp_is_input_request_method(const MCPProtocolVersion version,
                             const JSON::StringView method) noexcept -> bool {
   switch (version) {
@@ -1078,9 +1078,9 @@ mcp_is_input_request_method(const MCPProtocolVersion version,
 ///
 /// @see
 /// https://modelcontextprotocol.io/specification/2026-07-28/schema
-constexpr auto mcp_supports_method(const MCPProtocolVersion version,
-                                   const JSON::StringView method) noexcept
-    -> bool {
+[[nodiscard]] constexpr auto
+mcp_supports_method(const MCPProtocolVersion version,
+                    const JSON::StringView method) noexcept -> bool {
   switch (version) {
     case MCPProtocolVersion::V_2025_03_26:
       return method == MCP_METHOD_COMPLETION_COMPLETE ||
@@ -1202,8 +1202,8 @@ constexpr auto mcp_supports_method(const MCPProtocolVersion version,
 ///
 /// @see
 /// https://modelcontextprotocol.io/specification/2026-07-28/basic/patterns/mrtr
-constexpr auto mcp_is_mrtr_method(const JSON::StringView method) noexcept
-    -> bool {
+[[nodiscard]] constexpr auto
+mcp_is_mrtr_method(const JSON::StringView method) noexcept -> bool {
   return method == MCP_METHOD_TOOLS_CALL ||
          method == MCP_METHOD_RESOURCES_READ ||
          method == MCP_METHOD_PROMPTS_GET;
@@ -1223,8 +1223,8 @@ constexpr auto mcp_is_mrtr_method(const JSON::StringView method) noexcept
 ///
 /// @see
 /// https://modelcontextprotocol.io/specification/2026-07-28/server/utilities/caching#cacheable-results
-constexpr auto mcp_is_cacheable_method(const JSON::StringView method) noexcept
-    -> bool {
+[[nodiscard]] constexpr auto
+mcp_is_cacheable_method(const JSON::StringView method) noexcept -> bool {
   return method == MCP_METHOD_SERVER_DISCOVER ||
          method == MCP_METHOD_TOOLS_LIST || method == MCP_METHOD_PROMPTS_LIST ||
          method == MCP_METHOD_RESOURCES_LIST ||
@@ -1250,7 +1250,7 @@ constexpr auto mcp_is_cacheable_method(const JSON::StringView method) noexcept
 ///
 /// @see
 /// https://modelcontextprotocol.io/specification/2026-07-28/schema
-constexpr auto
+[[nodiscard]] constexpr auto
 mcp_is_client_notification_method(MCPProtocolVersion version,
                                   JSON::StringView method) noexcept -> bool {
   switch (version) {
@@ -1294,7 +1294,7 @@ mcp_is_client_notification_method(MCPProtocolVersion version,
 ///
 /// @see
 /// https://modelcontextprotocol.io/specification/2026-07-28/schema
-constexpr auto
+[[nodiscard]] constexpr auto
 mcp_is_server_notification_method(MCPProtocolVersion version,
                                   JSON::StringView method) noexcept -> bool {
   switch (version) {
diff --git a/src/core/mcp/include/sourcemeta/core/mcp_results.h b/src/core/mcp/include/sourcemeta/core/mcp_results.h
index 114ceb639..15db1c3f7 100644
--- a/src/core/mcp/include/sourcemeta/core/mcp_results.h
+++ b/src/core/mcp/include/sourcemeta/core/mcp_results.h
@@ -45,8 +45,8 @@ enum class MCPCacheScope : std::uint8_t {
 /// assert(sourcemeta::core::mcp_cache_scope_string(
 ///            sourcemeta::core::MCPCacheScope::Private) == "private");
 /// ```
-constexpr auto mcp_cache_scope_string(const MCPCacheScope scope) noexcept
-    -> JSON::StringView {
+[[nodiscard]] constexpr auto
+mcp_cache_scope_string(const MCPCacheScope scope) noexcept -> JSON::StringView {
   switch (scope) {
     case MCPCacheScope::Public:
       return "public";
@@ -73,7 +73,8 @@ constexpr auto mcp_cache_scope_string(const MCPCacheScope scope) noexcept
 ///        sourcemeta::core::MCPCacheScope::Private);
 /// assert(!sourcemeta::core::mcp_resolve_cache_scope("shared").has_value());
 /// ```
-constexpr auto mcp_resolve_cache_scope(const JSON::StringView scope) noexcept
+[[nodiscard]] constexpr auto
+mcp_resolve_cache_scope(const JSON::StringView scope) noexcept
     -> std::optional<MCPCacheScope> {
   if (scope == "public") {
     return MCPCacheScope::Public;
@@ -183,9 +184,9 @@ struct MCPDescriptorPresentation {
 ///
 /// @see
 /// https://modelcontextprotocol.io/specification/2026-07-28/schema#annotations
-SOURCEMETA_CORE_MCP_EXPORT
-auto mcp_serialize_resource_annotations(
-    MCPProtocolVersion version, const MCPResourceAnnotations &annotations)
+[[nodiscard]] SOURCEMETA_CORE_MCP_EXPORT auto
+mcp_serialize_resource_annotations(MCPProtocolVersion version,
+                                   const MCPResourceAnnotations &annotations)
     -> JSON;
 
 /// @ingroup mcp
@@ -215,11 +216,10 @@ auto mcp_serialize_resource_annotations(
 ///
 /// @see
 /// https://modelcontextprotocol.io/specification/2026-07-28/schema#imagecontent
-SOURCEMETA_CORE_MCP_EXPORT
-auto mcp_make_image_block(MCPProtocolVersion version, JSON::StringView data,
-                          JSON::StringView mime_type,
-                          const MCPResourceAnnotations &annotations = {})
-    -> JSON;
+[[nodiscard]] SOURCEMETA_CORE_MCP_EXPORT auto
+mcp_make_image_block(MCPProtocolVersion version, JSON::StringView data,
+                     JSON::StringView mime_type,
+                     const MCPResourceAnnotations &annotations = {}) -> JSON;
 /// @ingroup mcp
 /// Build a base64 audio block, with the same contracts as the image builder.
 /// For example:
@@ -240,11 +240,10 @@ auto mcp_make_image_block(MCPProtocolVersion version, JSON::StringView data,
 ///
 /// @see
 /// https://modelcontextprotocol.io/specification/2026-07-28/schema#audiocontent
-SOURCEMETA_CORE_MCP_EXPORT
-auto mcp_make_audio_block(MCPProtocolVersion version, JSON::StringView data,
-                          JSON::StringView mime_type,
-                          const MCPResourceAnnotations &annotations = {})
-    -> JSON;
+[[nodiscard]] SOURCEMETA_CORE_MCP_EXPORT auto
+mcp_make_audio_block(MCPProtocolVersion version, JSON::StringView data,
+                     JSON::StringView mime_type,
+                     const MCPResourceAnnotations &annotations = {}) -> JSON;
 /// @ingroup mcp
 /// Embed a checked text/blob resource-content entry in a content block. For
 /// example:
@@ -269,9 +268,9 @@ auto mcp_make_audio_block(MCPProtocolVersion version, JSON::StringView data,
 ///
 /// @see
 /// https://modelcontextprotocol.io/specification/2026-07-28/schema#embeddedresource
-SOURCEMETA_CORE_MCP_EXPORT
-auto mcp_make_embedded_resource(MCPProtocolVersion version, JSON resource,
-                                const MCPResourceAnnotations &annotations = {})
+[[nodiscard]] SOURCEMETA_CORE_MCP_EXPORT auto
+mcp_make_embedded_resource(MCPProtocolVersion version, JSON resource,
+                           const MCPResourceAnnotations &annotations = {})
     -> JSON;
 /// @ingroup mcp
 /// Build a blob resource-content entry. The caller supplies base64-encoded
@@ -292,10 +291,9 @@ auto mcp_make_embedded_resource(MCPProtocolVersion version, JSON resource,
 ///
 /// @see
 /// https://modelcontextprotocol.io/specification/2026-07-28/schema#blobresourcecontents
-SOURCEMETA_CORE_MCP_EXPORT
-auto mcp_make_resource_blob_content(JSON::StringView uri,
-                                    JSON::StringView mime_type,
-                                    JSON::StringView blob) -> JSON;
+[[nodiscard]] SOURCEMETA_CORE_MCP_EXPORT auto
+mcp_make_resource_blob_content(JSON::StringView uri, JSON::StringView mime_type,
+                               JSON::StringView blob) -> JSON;
 /// @ingroup mcp
 /// Build an MCP `text` content block carrying the given text payload. For
 /// example:
@@ -313,8 +311,8 @@ auto mcp_make_resource_blob_content(JSON::StringView uri,
 ///
 /// @see
 /// https://modelcontextprotocol.io/specification/2026-07-28/schema#textcontent
-SOURCEMETA_CORE_MCP_EXPORT
-auto mcp_make_text_block(const JSON::StringView text) -> sourcemeta::core::JSON;
+[[nodiscard]] SOURCEMETA_CORE_MCP_EXPORT auto
+mcp_make_text_block(const JSON::StringView text) -> sourcemeta::core::JSON;
 
 /// @ingroup mcp
 /// Build an MCP content block referencing a resource by URI. This block type
@@ -339,13 +337,10 @@ auto mcp_make_text_block(const JSON::StringView text) -> sourcemeta::core::JSON;
 ///
 /// @see
 /// https://modelcontextprotocol.io/specification/2026-07-28/schema#resourcelink
-SOURCEMETA_CORE_MCP_EXPORT
-auto mcp_make_resource_link(const MCPProtocolVersion version,
-                            const JSON::StringView uri,
-                            const JSON::StringView name,
-                            const JSON::StringView mime_type = {},
-                            const JSON::StringView description = {})
-    -> sourcemeta::core::JSON;
+[[nodiscard]] SOURCEMETA_CORE_MCP_EXPORT auto mcp_make_resource_link(
+    const MCPProtocolVersion version, const JSON::StringView uri,
+    const JSON::StringView name, const JSON::StringView mime_type = {},
+    const JSON::StringView description = {}) -> sourcemeta::core::JSON;
 
 /// @ingroup mcp
 /// Decorate a successful MCP result object with version-appropriate envelope
@@ -373,8 +368,7 @@ auto mcp_make_resource_link(const MCPProtocolVersion version,
 ///
 /// @see
 /// https://modelcontextprotocol.io/specification/2026-07-28/schema#result
-SOURCEMETA_CORE_MCP_EXPORT
-auto mcp_decorate_result(
+[[nodiscard]] SOURCEMETA_CORE_MCP_EXPORT auto mcp_decorate_result(
     const MCPProtocolVersion version, sourcemeta::core::JSON result,
     const std::optional<MCPImplementation> &server_info = std::nullopt)
     -> sourcemeta::core::JSON;
@@ -403,11 +397,9 @@ auto mcp_decorate_result(
 ///
 /// @see
 /// https://modelcontextprotocol.io/specification/2026-07-28/server/utilities/caching#cacheable-results
-SOURCEMETA_CORE_MCP_EXPORT
-auto mcp_decorate_cacheable_result(const MCPProtocolVersion version,
-                                   sourcemeta::core::JSON result,
-                                   const MCPCachePolicy &cache_policy,
-                                   const JSON::StringView method)
+[[nodiscard]] SOURCEMETA_CORE_MCP_EXPORT auto mcp_decorate_cacheable_result(
+    const MCPProtocolVersion version, sourcemeta::core::JSON result,
+    const MCPCachePolicy &cache_policy, const JSON::StringView method)
     -> sourcemeta::core::JSON;
 
 /// @ingroup mcp
@@ -439,8 +431,7 @@ auto mcp_decorate_cacheable_result(const MCPProtocolVersion version,
 /// https://modelcontextprotocol.io/specification/2026-07-28/schema#emptyresult
 /// @see
 /// https://modelcontextprotocol.io/specification/2026-07-28/schema#jsonrpcresultresponse
-SOURCEMETA_CORE_MCP_EXPORT
-auto mcp_make_empty_response(
+[[nodiscard]] SOURCEMETA_CORE_MCP_EXPORT auto mcp_make_empty_response(
     const MCPProtocolVersion version, const sourcemeta::core::JSON &identifier,
     const std::optional<MCPImplementation> &server_info = std::nullopt)
     -> sourcemeta::core::JSON;
@@ -474,8 +465,7 @@ auto mcp_make_empty_response(
 ///
 /// @see
 /// https://modelcontextprotocol.io/specification/2026-07-28/server/tools
-SOURCEMETA_CORE_MCP_EXPORT
-auto mcp_make_tool_success(
+[[nodiscard]] SOURCEMETA_CORE_MCP_EXPORT auto mcp_make_tool_success(
     const MCPProtocolVersion version, const sourcemeta::core::JSON &identifier,
     sourcemeta::core::JSON result,
     const std::optional<MCPImplementation> &server_info = std::nullopt)
@@ -511,8 +501,7 @@ auto mcp_make_tool_success(
 ///
 /// @see
 /// https://modelcontextprotocol.io/specification/2026-07-28/server/tools
-SOURCEMETA_CORE_MCP_EXPORT
-auto mcp_make_tool_success(
+[[nodiscard]] SOURCEMETA_CORE_MCP_EXPORT auto mcp_make_tool_success(
     const MCPProtocolVersion version, const sourcemeta::core::JSON &identifier,
     sourcemeta::core::JSON structured, sourcemeta::core::JSON content_blocks,
     const std::optional<MCPImplementation> &server_info = std::nullopt)
@@ -543,8 +532,7 @@ auto mcp_make_tool_success(
 ///
 /// @see
 /// https://modelcontextprotocol.io/specification/2026-07-28/server/tools#error-handling
-SOURCEMETA_CORE_MCP_EXPORT
-auto mcp_make_tool_error(
+[[nodiscard]] SOURCEMETA_CORE_MCP_EXPORT auto mcp_make_tool_error(
     const MCPProtocolVersion version, const sourcemeta::core::JSON &identifier,
     const JSON::StringView message,
     const std::optional<MCPImplementation> &server_info = std::nullopt)
@@ -571,15 +559,14 @@ auto mcp_make_tool_error(
 ///
 /// @see
 /// https://modelcontextprotocol.io/specification/2026-07-28/schema#resource
-SOURCEMETA_CORE_MCP_EXPORT
-auto mcp_make_resource(const MCPProtocolVersion version,
-                       const JSON::StringView uri, const JSON::StringView name,
-                       const JSON::StringView mime_type,
-                       const JSON::StringView description = {},
-                       const std::optional<std::size_t> size = std::nullopt,
-                       const std::optional<double> priority = std::nullopt,
-                       const MCPDescriptorPresentation &presentation = {},
-                       const MCPResourceAnnotations &annotations = {})
+[[nodiscard]] SOURCEMETA_CORE_MCP_EXPORT auto
+mcp_make_resource(const MCPProtocolVersion version, const JSON::StringView uri,
+                  const JSON::StringView name, const JSON::StringView mime_type,
+                  const JSON::StringView description = {},
+                  const std::optional<std::size_t> size = std::nullopt,
+                  const std::optional<double> priority = std::nullopt,
+                  const MCPDescriptorPresentation &presentation = {},
+                  const MCPResourceAnnotations &annotations = {})
     -> sourcemeta::core::JSON;
 
 /// @ingroup mcp
@@ -601,11 +588,9 @@ auto mcp_make_resource(const MCPProtocolVersion version,
 ///
 /// @see
 /// https://modelcontextprotocol.io/specification/2026-07-28/schema#textresourcecontents
-SOURCEMETA_CORE_MCP_EXPORT
-auto mcp_make_resource_text_content(const JSON::StringView uri,
-                                    const JSON::StringView mime_type,
-                                    const JSON::StringView text)
-    -> sourcemeta::core::JSON;
+[[nodiscard]] SOURCEMETA_CORE_MCP_EXPORT auto mcp_make_resource_text_content(
+    const JSON::StringView uri, const JSON::StringView mime_type,
+    const JSON::StringView text) -> sourcemeta::core::JSON;
 
 /// @ingroup mcp
 /// Wrap a pre-built array of content entries into the MCP `resources/read`
@@ -635,11 +620,9 @@ auto mcp_make_resource_text_content(const JSON::StringView uri,
 ///
 /// @see
 /// https://modelcontextprotocol.io/specification/2026-07-28/server/resources
-SOURCEMETA_CORE_MCP_EXPORT
-auto mcp_make_resources_read_result(const MCPProtocolVersion version,
-                                    sourcemeta::core::JSON contents,
-                                    const MCPCachePolicy &cache_policy)
-    -> sourcemeta::core::JSON;
+[[nodiscard]] SOURCEMETA_CORE_MCP_EXPORT auto mcp_make_resources_read_result(
+    const MCPProtocolVersion version, sourcemeta::core::JSON contents,
+    const MCPCachePolicy &cache_policy) -> sourcemeta::core::JSON;
 
 /// @ingroup mcp
 /// Build a single entry for an MCP `resources/templates/list` response. For
@@ -663,8 +646,7 @@ auto mcp_make_resources_read_result(const MCPProtocolVersion version,
 ///
 /// @see
 /// https://modelcontextprotocol.io/specification/2026-07-28/schema#resourcetemplate
-SOURCEMETA_CORE_MCP_EXPORT
-auto mcp_make_resource_template(
+[[nodiscard]] SOURCEMETA_CORE_MCP_EXPORT auto mcp_make_resource_template(
     const MCPProtocolVersion version, const JSON::StringView uri_template,
     const JSON::StringView name, const JSON::StringView description,
     const JSON::StringView mime_type,
@@ -702,8 +684,7 @@ auto mcp_make_resource_template(
 ///
 /// @see
 /// https://modelcontextprotocol.io/specification/2026-07-28/schema#tool
-SOURCEMETA_CORE_MCP_EXPORT
-auto mcp_make_tool_descriptor(
+[[nodiscard]] SOURCEMETA_CORE_MCP_EXPORT auto mcp_make_tool_descriptor(
     const MCPProtocolVersion version, const JSON::StringView name,
     const JSON::StringView description, sourcemeta::core::JSON input_schema,
     std::optional<sourcemeta::core::JSON> output_schema = std::nullopt,
@@ -735,8 +716,7 @@ auto mcp_make_tool_descriptor(
 ///
 /// @see
 /// https://modelcontextprotocol.io/specification/2026-07-28/server/utilities/caching#cacheable-results
-SOURCEMETA_CORE_MCP_EXPORT
-auto mcp_make_tools_list_result(
+[[nodiscard]] SOURCEMETA_CORE_MCP_EXPORT auto mcp_make_tools_list_result(
     const MCPProtocolVersion version, sourcemeta::core::JSON tools,
     const std::optional<JSON::StringView> next_cursor,
     const MCPCachePolicy &cache_policy) -> sourcemeta::core::JSON;
@@ -771,8 +751,7 @@ auto mcp_make_tools_list_result(
 ///
 /// @see
 /// https://modelcontextprotocol.io/specification/2026-07-28/server/utilities/caching#cacheable-results
-SOURCEMETA_CORE_MCP_EXPORT
-auto mcp_make_resources_list_result(
+[[nodiscard]] SOURCEMETA_CORE_MCP_EXPORT auto mcp_make_resources_list_result(
     const MCPProtocolVersion version, sourcemeta::core::JSON resources,
     const std::optional<JSON::StringView> next_cursor,
     const MCPCachePolicy &cache_policy) -> sourcemeta::core::JSON;
@@ -801,8 +780,8 @@ auto mcp_make_resources_list_result(
 ///
 /// @see
 /// https://modelcontextprotocol.io/specification/2026-07-28/server/utilities/caching#cacheable-results
-SOURCEMETA_CORE_MCP_EXPORT
-auto mcp_make_resource_templates_list_result(
+[[nodiscard]] SOURCEMETA_CORE_MCP_EXPORT auto
+mcp_make_resource_templates_list_result(
     const MCPProtocolVersion version, sourcemeta::core::JSON resource_templates,
     const std::optional<JSON::StringView> next_cursor,
     const MCPCachePolicy &cache_policy) -> sourcemeta::core::JSON;
@@ -833,8 +812,7 @@ auto mcp_make_resource_templates_list_result(
 ///
 /// @see
 /// https://modelcontextprotocol.io/specification/2026-07-28/server/utilities/caching#cacheable-results
-SOURCEMETA_CORE_MCP_EXPORT
-auto mcp_make_prompts_list_result(
+[[nodiscard]] SOURCEMETA_CORE_MCP_EXPORT auto mcp_make_prompts_list_result(
     const MCPProtocolVersion version, sourcemeta::core::JSON prompts,
     const std::optional<JSON::StringView> next_cursor,
     const MCPCachePolicy &cache_policy) -> sourcemeta::core::JSON;
@@ -869,9 +847,9 @@ auto mcp_make_prompts_list_result(
 ///
 /// @see
 /// https://modelcontextprotocol.io/specification/2026-07-28/server/prompts
-SOURCEMETA_CORE_MCP_EXPORT
-auto mcp_make_prompts_get_result(MCPProtocolVersion version,
-                                 JSON::StringView description, JSON messages)
+[[nodiscard]] SOURCEMETA_CORE_MCP_EXPORT auto
+mcp_make_prompts_get_result(MCPProtocolVersion version,
+                            JSON::StringView description, JSON messages)
     -> JSON;
 
 /// @ingroup mcp
@@ -893,10 +871,10 @@ auto mcp_make_prompts_get_result(MCPProtocolVersion version,
 ///
 /// @see
 /// https://modelcontextprotocol.io/specification/2026-07-28/schema#completeresult
-SOURCEMETA_CORE_MCP_EXPORT
-auto mcp_make_completion_result(MCPProtocolVersion version, JSON values,
-                                std::optional<std::int64_t> total,
-                                std::optional<bool> has_more) -> JSON;
+[[nodiscard]] SOURCEMETA_CORE_MCP_EXPORT auto
+mcp_make_completion_result(MCPProtocolVersion version, JSON values,
+                           std::optional<std::int64_t> total,
+                           std::optional<bool> has_more) -> JSON;
 
 /// @ingroup mcp
 /// Serialize a complete MCP response for one of the six cacheable operations.
@@ -1005,8 +983,7 @@ auto mcp_write_result(
 ///
 /// @see
 /// https://modelcontextprotocol.io/specification/2025-11-25/basic/lifecycle#initialization
-SOURCEMETA_CORE_MCP_EXPORT
-auto mcp_make_initialize_response(
+[[nodiscard]] SOURCEMETA_CORE_MCP_EXPORT auto mcp_make_initialize_response(
     const sourcemeta::core::JSON &request,
     const MCPServerCapabilities &capabilities, const MCPImplementation &server,
     const std::span<const JSON::StringView> supported_versions,
@@ -1045,8 +1022,7 @@ auto mcp_make_initialize_response(
 ///
 /// @see
 /// https://modelcontextprotocol.io/specification/2026-07-28/schema#discoverresult
-SOURCEMETA_CORE_MCP_EXPORT
-auto mcp_make_server_discover_response(
+[[nodiscard]] SOURCEMETA_CORE_MCP_EXPORT auto mcp_make_server_discover_response(
     const MCPProtocolVersion version, const sourcemeta::core::JSON &identifier,
     const MCPServerCapabilities &capabilities, const MCPImplementation &server,
     const std::span<const JSON::StringView> supported_versions,
@@ -1098,8 +1074,7 @@ auto mcp_make_server_discover_response(
 ///
 /// @see
 /// https://modelcontextprotocol.io/specification/2026-07-28/basic/patterns/mrtr#supported-requests
-SOURCEMETA_CORE_MCP_EXPORT
-auto mcp_make_input_required_response(
+[[nodiscard]] SOURCEMETA_CORE_MCP_EXPORT auto mcp_make_input_required_response(
     const MCPProtocolVersion version, const JSON::StringView method,
     const sourcemeta::core::JSON &identifier,
     std::optional<sourcemeta::core::JSON> input_requests,
@@ -1136,9 +1111,9 @@ auto mcp_make_input_required_response(
 ///
 /// @see
 /// https://modelcontextprotocol.io/specification/2026-07-28/basic/patterns/mrtr
-SOURCEMETA_CORE_MCP_EXPORT
-auto mcp_request_input_responses(MCPProtocolVersion version,
-                                 const sourcemeta::core::JSON &envelope)
+[[nodiscard]] SOURCEMETA_CORE_MCP_EXPORT auto
+mcp_request_input_responses(MCPProtocolVersion version,
+                            const sourcemeta::core::JSON &envelope)
     -> const sourcemeta::core::JSON *;
 
 /// @ingroup mcp
@@ -1162,9 +1137,9 @@ auto mcp_request_input_responses(MCPProtocolVersion version,
 ///
 /// @see
 /// https://modelcontextprotocol.io/specification/2026-07-28/basic/patterns/mrtr
-SOURCEMETA_CORE_MCP_EXPORT
-auto mcp_request_state(MCPProtocolVersion version,
-                       const sourcemeta::core::JSON &envelope)
+[[nodiscard]] SOURCEMETA_CORE_MCP_EXPORT auto
+mcp_request_state(MCPProtocolVersion version,
+                  const sourcemeta::core::JSON &envelope)
     -> std::optional<JSON::StringView>;
 
 /// @ingroup mcp
@@ -1215,9 +1190,9 @@ struct MCPSubscriptionFilter {
 ///
 /// @see
 /// https://modelcontextprotocol.io/specification/2026-07-28/basic/patterns/subscriptions
-SOURCEMETA_CORE_MCP_EXPORT
-auto mcp_parse_subscription_filter(MCPProtocolVersion version,
-                                   const JSON &parameters)
+[[nodiscard]] SOURCEMETA_CORE_MCP_EXPORT auto
+mcp_parse_subscription_filter(MCPProtocolVersion version,
+                              const JSON &parameters)
     -> std::optional<MCPSubscriptionFilter>;
 
 /// @ingroup mcp
@@ -1242,9 +1217,9 @@ auto mcp_parse_subscription_filter(MCPProtocolVersion version,
 ///
 /// @see
 /// https://modelcontextprotocol.io/specification/2026-07-28/basic/patterns/subscriptions
-SOURCEMETA_CORE_MCP_EXPORT
-auto mcp_intersect_subscription_filters(const MCPSubscriptionFilter &requested,
-                                        const MCPSubscriptionFilter &supported)
+[[nodiscard]] SOURCEMETA_CORE_MCP_EXPORT auto
+mcp_intersect_subscription_filters(const MCPSubscriptionFilter &requested,
+                                   const MCPSubscriptionFilter &supported)
     -> MCPSubscriptionFilter;
 
 /// @ingroup mcp
@@ -1269,8 +1244,8 @@ auto mcp_intersect_subscription_filters(const MCPSubscriptionFilter &requested,
 ///
 /// @see
 /// https://modelcontextprotocol.io/specification/2026-07-28/basic/index#result-responses
-SOURCEMETA_CORE_MCP_EXPORT
-auto mcp_result_type(const JSON &result) -> std::optional<JSON::StringView>;
+[[nodiscard]] SOURCEMETA_CORE_MCP_EXPORT auto
+mcp_result_type(const JSON &result) -> std::optional<JSON::StringView>;
 
 /// @ingroup mcp
 /// Recognize base and explicitly negotiated extension result types. The
@@ -1299,8 +1274,7 @@ auto mcp_result_type(const JSON &result) -> std::optional<JSON::StringView>;
 ///
 /// @see
 /// https://modelcontextprotocol.io/specification/2026-07-28/basic/index#result-responses
-SOURCEMETA_CORE_MCP_EXPORT
-auto mcp_resolve_result_type(
+[[nodiscard]] SOURCEMETA_CORE_MCP_EXPORT auto mcp_resolve_result_type(
     MCPProtocolVersion version, const JSON &result,
     std::span<const JSON::StringView> supported_extension_types = {})
     -> std::optional<JSON::StringView>;
@@ -1344,10 +1318,9 @@ auto mcp_resolve_result_type(
 ///
 /// @see
 /// https://modelcontextprotocol.io/specification/2026-07-28/basic/patterns/mrtr#client-requirements-basic-workflow
-SOURCEMETA_CORE_MCP_EXPORT
-auto mcp_validate_continuation(MCPProtocolVersion version,
-                               const JSON &parameters,
-                               const JSON &input_requests) -> bool;
+[[nodiscard]] SOURCEMETA_CORE_MCP_EXPORT auto
+mcp_validate_continuation(MCPProtocolVersion version, const JSON &parameters,
+                          const JSON &input_requests) -> bool;
 
 /// @ingroup mcp
 /// Check continuation fields and the state token, where the expected state
@@ -1382,11 +1355,10 @@ auto mcp_validate_continuation(MCPProtocolVersion version,
 ///
 /// @see
 /// https://modelcontextprotocol.io/specification/2026-07-28/basic/patterns/mrtr
-SOURCEMETA_CORE_MCP_EXPORT
-auto mcp_validate_continuation(MCPProtocolVersion version,
-                               const JSON &parameters,
-                               const JSON &input_requests,
-                               std::optional<JSON::StringView> expected_state)
+[[nodiscard]] SOURCEMETA_CORE_MCP_EXPORT auto
+mcp_validate_continuation(MCPProtocolVersion version, const JSON &parameters,
+                          const JSON &input_requests,
+                          std::optional<JSON::StringView> expected_state)
     -> bool;
 
 /// @ingroup mcp
@@ -1419,13 +1391,12 @@ auto mcp_validate_continuation(MCPProtocolVersion version,
 ///
 /// @see
 /// https://modelcontextprotocol.io/specification/2026-07-28/basic/patterns/subscriptions
-SOURCEMETA_CORE_MCP_EXPORT
-auto mcp_make_notification(MCPProtocolVersion version, bool from_server,
-                           JSON::StringView method, JSON parameters,
-                           std::optional<JSON> subscription_id,
-                           const MCPSubscriptionFilter *acknowledged = nullptr,
-                           const MCPRequestMeta *request_context = nullptr)
-    -> JSON;
+[[nodiscard]] SOURCEMETA_CORE_MCP_EXPORT auto
+mcp_make_notification(MCPProtocolVersion version, bool from_server,
+                      JSON::StringView method, JSON parameters,
+                      std::optional<JSON> subscription_id,
+                      const MCPSubscriptionFilter *acknowledged = nullptr,
+                      const MCPRequestMeta *request_context = nullptr) -> JSON;
 
 /// @ingroup mcp
 /// Build an acknowledgement notification for `subscriptions/listen` with a
@@ -1454,8 +1425,8 @@ auto mcp_make_notification(MCPProtocolVersion version, bool from_server,
 ///
 /// @see
 /// https://modelcontextprotocol.io/specification/2026-07-28/basic/patterns/subscriptions
-SOURCEMETA_CORE_MCP_EXPORT
-auto mcp_make_subscription_acknowledged_notification(
+[[nodiscard]] SOURCEMETA_CORE_MCP_EXPORT auto
+mcp_make_subscription_acknowledged_notification(
     const MCPProtocolVersion version,
     const sourcemeta::core::JSON &subscription_id,
     const MCPSubscriptionFilter &requested,
@@ -1486,8 +1457,8 @@ auto mcp_make_subscription_acknowledged_notification(
 ///
 /// @see
 /// https://modelcontextprotocol.io/specification/2026-07-28/basic/patterns/subscriptions
-SOURCEMETA_CORE_MCP_EXPORT
-auto mcp_make_subscription_acknowledged_notification(
+[[nodiscard]] SOURCEMETA_CORE_MCP_EXPORT auto
+mcp_make_subscription_acknowledged_notification(
     const MCPProtocolVersion version, const JSON::StringView subscription_id,
     const MCPSubscriptionFilter &requested,
     const MCPSubscriptionFilter &supported) -> sourcemeta::core::JSON;
@@ -1508,8 +1479,8 @@ auto mcp_make_subscription_acknowledged_notification(
 ///
 /// @see
 /// https://modelcontextprotocol.io/specification/2026-07-28/basic/patterns/subscriptions
-SOURCEMETA_CORE_MCP_EXPORT
-auto mcp_make_subscription_close_response(
+[[nodiscard]] SOURCEMETA_CORE_MCP_EXPORT auto
+mcp_make_subscription_close_response(
     const MCPProtocolVersion version, const sourcemeta::core::JSON &identifier,
     const std::optional<MCPImplementation> &server_info = std::nullopt)
     -> sourcemeta::core::JSON;
@@ -1537,9 +1508,9 @@ auto mcp_make_subscription_close_response(
 ///
 /// @see
 /// https://modelcontextprotocol.io/specification/2026-07-28/basic/patterns/subscriptions
-SOURCEMETA_CORE_MCP_EXPORT
-auto mcp_request_subscription_id(MCPProtocolVersion version,
-                                 const sourcemeta::core::JSON &envelope)
+[[nodiscard]] SOURCEMETA_CORE_MCP_EXPORT auto
+mcp_request_subscription_id(MCPProtocolVersion version,
+                            const sourcemeta::core::JSON &envelope)
     -> const sourcemeta::core::JSON *;
 
 /// @ingroup mcp
@@ -1564,8 +1535,8 @@ auto mcp_request_subscription_id(MCPProtocolVersion version,
 ///
 /// @see
 /// https://modelcontextprotocol.io/specification/2026-07-28/server/tools
-SOURCEMETA_CORE_MCP_EXPORT
-auto mcp_tool_call_arguments(const sourcemeta::core::JSON &envelope)
+[[nodiscard]] SOURCEMETA_CORE_MCP_EXPORT auto
+mcp_tool_call_arguments(const sourcemeta::core::JSON &envelope)
     -> const sourcemeta::core::JSON *;
 
 } // namespace sourcemeta::core
diff --git a/src/core/mcp/validation.h b/src/core/mcp/validation.h
index 53accb05a..1c2436691 100644
--- a/src/core/mcp/validation.h
+++ b/src/core/mcp/validation.h
@@ -165,12 +165,6 @@ inline auto icon_size(const JSON::StringView value) -> bool {
          });
 }
 
-inline auto strings(const JSON &value) -> bool {
-  return value.is_array() &&
-         std::all_of(value.as_array().begin(), value.as_array().end(),
-                     [](const auto &item) { return item.is_string(); });
-}
-
 inline auto annotations(const JSON &value, const bool received = false)
     -> bool {
   const auto *item{
@@ -194,11 +188,12 @@ inline auto annotations(const JSON &value, const bool received = false)
   if (const auto *audience{
           field(*item, "audience", sourcemeta::core::MCP_HASH_AUDIENCE)};
       audience != nullptr) {
-    if (!strings(*audience)) {
+    if (!audience->is_array_of_strings()) {
       return false;
     }
     for (const auto &role : audience->as_array()) {
-      if (role.to_string() != "user" && role.to_string() != "assistant") {
+      const auto &role_name{role.to_string()};
+      if (role_name != "user" && role_name != "assistant") {
         return false;
       }
     }
@@ -228,7 +223,7 @@ inline auto icons(const JSON &value, const bool received = false) -> bool {
     if (const auto *sizes{
             field(item, "sizes", sourcemeta::core::MCP_HASH_SIZES)};
         sizes != nullptr) {
-      if (!strings(*sizes)) {
+      if (!sizes->is_array_of_strings()) {
         return false;
       }
 
@@ -240,10 +235,14 @@ inline auto icons(const JSON &value, const bool received = false) -> bool {
     }
     if (const auto *theme{
             field(item, "theme", sourcemeta::core::MCP_HASH_THEME)};
-        (theme != nullptr) &&
-        (!theme->is_string() ||
-         (theme->to_string() != "light" && theme->to_string() != "dark"))) {
-      return false;
+        theme != nullptr) {
+      if (!theme->is_string()) {
+        return false;
+      }
+      const auto &theme_name{theme->to_string()};
+      if (theme_name != "light" && theme_name != "dark") {
+        return false;
+      }
     }
   }
   return true;
@@ -361,7 +360,7 @@ inline auto sampling_block(const JSON &value, const bool received = false)
                                               value)) {
     return false;
   }
-  const auto name{type->to_string()};
+  const auto &name{type->to_string()};
   if (name == "text" || name == "image" || name == "audio") {
     return sourcemeta::core::internal::valid_content(
         MCPProtocolVersion::V_2026_07_28, value, received);
@@ -402,7 +401,7 @@ inline auto sampling_message_block(const JSON &block, const bool tools,
   if (!sampling_block(block)) {
     return false;
   }
-  const auto type{
+  const auto &type{
       block.at("type", sourcemeta::core::MCP_HASH_TYPE).to_string()};
   if (type == "tool_result") {
     return tools && answering && role == "user" &&
@@ -484,7 +483,7 @@ inline auto sampling_options(const JSON &params) -> bool {
   }
   if (const auto *stop{field(params, "stopSequences",
                              sourcemeta::core::MCP_HASH_STOP_SEQUENCES)};
-      (stop != nullptr) && !strings(*stop)) {
+      (stop != nullptr) && !stop->is_array_of_strings()) {
     return false;
   }
   if (const auto *choice{
@@ -914,7 +913,7 @@ inline auto valid_resource(const MCPProtocolVersion version, const JSON &value,
       validation::field(value, "size", sourcemeta::core::MCP_HASH_SIZE)};
   return validation::base(value, received) &&
          validation::annotations(value, received) &&
-         ((size == nullptr) || (size->is_integral() && *size >= JSON{0}));
+         ((size == nullptr) || (size->is_integral() && size->is_positive()));
 }
 
 inline auto valid_content(const MCPProtocolVersion version, const JSON &value,
@@ -928,7 +927,7 @@ inline auto valid_content(const MCPProtocolVersion version, const JSON &value,
   if ((type == nullptr) || !type->is_string()) {
     return false;
   }
-  const auto name{type->to_string()};
+  const auto &name{type->to_string()};
   if (name == "text") {
     return validation::string_field(value, "text",
                                     sourcemeta::core::MCP_HASH_TEXT, true);
@@ -1002,7 +1001,7 @@ inline auto valid_input_requests(const JSON &value,
          !valid_meta(MCPProtocolVersion::V_2026_07_28, *params))) {
       return false;
     }
-    const auto name{method->to_string()};
+    const auto &name{method->to_string()};
     if (name == MCP_METHOD_ROOTS_LIST) {
       if (!capabilities.roots) {
         return false;
@@ -1147,7 +1146,7 @@ inline auto valid_input_response(const JSON::StringView method,
       }
       for (const auto &entry : content->as_object()) {
         if (!entry.second.is_string() && !entry.second.is_number() &&
-            !entry.second.is_boolean() && !validation::strings(entry.second)) {
+            !entry.second.is_boolean() && !entry.second.is_array_of_strings()) {
           return false;
         }
       }
diff --git a/test/mcp/mcp_error_test.cc b/test/mcp/mcp_error_test.cc
index 0b22b8151..1858930eb 100644
--- a/test/mcp/mcp_error_test.cc
+++ b/test/mcp/mcp_error_test.cc
@@ -1144,8 +1144,8 @@ TEST(error_code_to_http_status_unmapped_code) {
 
 TEST(mcp_error_is_catchable_as_an_invalid_argument) {
   try {
-    sourcemeta::core::mcp_make_resource_link(
-        sourcemeta::core::MCPProtocolVersion::V_2025_03_26, "file:///a", "a");
+    static_cast<void>(sourcemeta::core::mcp_make_resource_link(
+        sourcemeta::core::MCPProtocolVersion::V_2025_03_26, "file:///a", "a"));
     FAIL();
   } catch (const std::invalid_argument &error) {
     EXPECT_STREQ(error.what(),
diff --git a/test/mcp/mcp_helpers.h b/test/mcp/mcp_helpers.h
index 690d70f6f..142809a82 100644
--- a/test/mcp/mcp_helpers.h
+++ b/test/mcp/mcp_helpers.h
@@ -11,7 +11,7 @@
 // expectation is re-raised so that it is not mistaken for a rejection
 #define EXPECT_MCP_REJECTS(expression, expected_message)                       \
   try {                                                                        \
-    expression;                                                                \
+    static_cast<void>(expression);                                             \
     FAIL();                                                                    \
   } catch (const ::sourcemeta::core::MCPError &sourcemeta_test_error) {        \
     EXPECT_STREQ(sourcemeta_test_error.what(), expected_message);              \