feat: support structured output in JSON Schema over A2A DataPart by supreme-gg-gg · Pull Request #2890 · kagent-dev/kagent

supreme-gg-gg · 2026-09-21T22:55:38Z

Summary

This feature is only supported in Kagent's own harness, not yet in Claude / Codex

Add inline and ConfigMap-backed output schemas to ADK agent templates.
Validate schemas against a portable provider-compatible JSON Schema profile.
Support structured output with tools across OpenAI, Anthropic, Bedrock, and Gemini through ADK.
Validate final responses and publish them as JSON A2A artifacts with schema metadata.
Add unit and E2E coverage for tool calls and partial streaming responses.
Document the structured-output design and provider behavior.
Relevant UI changes to configure output mode, display structured output, etc

Testing

Unit and E2E tests
Manual testing on OpenAI (Chat completion + Responses), Gemini (API), Claude (Bedrock)
Tested with both tool using and structured output

supreme-gg-gg · 2026-09-22T02:46:04Z

First image: UI for using tool call with structured output

Second image: AgentTemplate details page showing the agent's structured output schema

Third image: Gemini models might (depending on version) use an additional tool to set structured output. This is done internally by ADK and is a known workaround for some older model that does not support tool calling with structured output.

EItanya · 2026-09-22T10:29:04Z

 	A2ADataPartMetadataIsLongRunningKey     = "is_long_running"
 	A2ADataPartMetadataTypeFunctionCall     = "function_call"
 	A2ADataPartMetadataTypeFunctionResponse = "function_response"
+	OutputSchemaSHA256MetadataKey           = "kagent.dev/output-schema-sha256"


We used to have a KagentMetadata fn which prepended this key, do we still have that?

That function uses the kagent_ prefix for ADK function metadata these are public A2A result metadata like kagent.dev/timeline-position

Maybe we should still have functions to make sure they use the correct prefix. Also maybe the prefix should be kagent.dev/a2a?

I agree, I'll add both. I also think it's worth doing a follow-up to review the metadata before we do a stable release so we can still centralize and change them (e.g. we will want to change the timeline position above as well, and some legacy ADK metadata are no longer necessary, and probably renaming the adk_ and kagent_ ones)

I have a follow up for A2A metadata in #2902 if you want to take a quick look first, not fully ready for review yet

Charlesthebird

This automated review is a first pass. A manual review will follow once the blockers are addressed.

Two things block merge, both in transformStructuredOutput. The finish-reason guard added this round rejects an empty reason, which is what ADK's set_model_response path produces — the Gemini-with-tools case in the third screenshot. Separately, a HITL approval request still reaches the transform, where it has no text to validate and fails the task.

⚠️ What I checked

✅ AfterEventCallback fires only for a non-nil A2A event, and its error becomes a failed task — adk@v2.3.0 server/adka2a/v2/executor.go:366-375.
✅ The CEL rule making outputSchema and outputSchemaFrom mutually exclusive is on AgentTemplateSpec.
✅ outputSchemaFrom is added to the provenance ConfigMap set, so editing the ConfigMap recompiles the revision.
✅ Cycle detection uses pointer identity after $ref resolution, so A → B → A is caught.
✅ The canonical form re-marshals through map[string]any, so the digest is stable across key order.
⚠️ IsFinalResponse() short-circuits to true on LongRunningToolIDs and SkipSummarization — adk@v2.3.0 session/session.go:225.
⚠️ ADK builds the set_model_response final event with no finish reason — adk@v2.3.0 internal/llminternal/outputschema_processor.go:67-76.

🤖 written by Claude

Charlesthebird

The UI changes here LGTM - thanks for the screenshots! I also kicked off an automated review.

And I added #2894 as a follow-up issue since the chat message part renderers might be a good place for extension points.

supreme-gg-gg · 2026-09-22T19:16:55Z

Thanks for the review @Charlesthebird and I've also verified now structured output works with HITL:

Screen.Recording.2026-09-22.at.3.05.55.PM.mov

moezdil · 2026-09-22T21:07:47Z

-func NewKAgentExecutor(cfg KAgentExecutorConfig) *KAgentExecutor {
+// NewKAgentExecutor creates a KAgentExecutor from config. It returns an error if
+// the configured output schema cannot be prepared for runtime validation.
+func NewKAgentExecutor(cfg KAgentExecutorConfig) (*KAgentExecutor, error) {


#2896 also rewrites this callback, conflicts on merge

Hey @mesutoezdil can you avoid leaving this type of comments since they're not too constructive. Merge conflicts are natural and authors are expected to rebase on top, this simply adds more noise during reviews. Unless the changes across PRs are going in opposite directions, in which case it might be worthwhile to bring the author's attention to it and drive some discussion, otherwise this type of comment don't add any value, as in the case here and in a few other PRs that you left similar comments before.

fair point, noted 👍🏽 thx for feedback

Signed-off-by: Jet Chiang <pokyuen.jetchiang-ext@solo.io>

…ntent config and adk validation Signed-off-by: Jet Chiang <pokyuen.jetchiang-ext@solo.io>

Signed-off-by: Jet Chiang <pokyuen.jetchiang-ext@solo.io>

…-fail-task-on-max-tokens NewKAgentExecutor now returns an error too; the output-limit test checks it. Signed-off-by: Jose Armesto <github@armesto.net>

…ent-dev#2890) ## Summary > This feature is only supported in Kagent's own harness, not yet in Claude / Codex - Add inline and ConfigMap-backed output schemas to ADK agent templates. - Validate schemas against a portable provider-compatible JSON Schema profile. - Support structured output with tools across OpenAI, Anthropic, Bedrock, and Gemini through ADK. - Validate final responses and publish them as JSON A2A artifacts with schema metadata. - Add unit and E2E coverage for tool calls and partial streaming responses. - Document the structured-output design and provider behavior. - Relevant UI changes to configure output mode, display structured output, etc ## Testing - Unit and E2E tests - Manual testing on OpenAI (Chat completion + Responses), Gemini (API), Claude (Bedrock) - Tested with both tool using and structured output --------- Signed-off-by: Jet Chiang <pokyuen.jetchiang-ext@solo.io>

github-actions Bot added enhancement New feature or request and removed enhancement New feature or request labels Sep 21, 2026

This comment has been minimized.

Sign in to view

github-actions Bot added enhancement New feature or request and removed enhancement New feature or request labels Sep 22, 2026

supreme-gg-gg marked this pull request as ready for review September 22, 2026 02:48

supreme-gg-gg requested review from a team, Charlesthebird and peterj as code owners September 22, 2026 02:48

EItanya reviewed Sep 22, 2026

View reviewed changes

Charlesthebird mentioned this pull request Sep 22, 2026

[FEATURE] Let an app extension replace a chat message part renderer #2894

Closed

supreme-gg-gg force-pushed the jetc/feat/structured-output branch from b36d743 to 5521dfa Compare September 22, 2026 17:25

Charlesthebird reviewed Sep 22, 2026

View reviewed changes

moezdil reviewed Sep 22, 2026

View reviewed changes

moezdil mentioned this pull request Sep 22, 2026

fix(adk): fail the task when the model stops at max_tokens instead of completing with a cut answer #2896

Open

Charlesthebird approved these changes Sep 22, 2026

View reviewed changes

supreme-gg-gg added this pull request to stack #2903 September 22, 2026 22:35

supreme-gg-gg added 7 commits September 22, 2026 18:37

go adk: model providers support

191d515

Signed-off-by: Jet Chiang <pokyuen.jetchiang-ext@solo.io>

crd

3ad2baf

Signed-off-by: Jet Chiang <pokyuen.jetchiang-ext@solo.io>

translator, outputschema validation, agent config and llm generate co…

25bc8a0

…ntent config and adk validation Signed-off-by: Jet Chiang <pokyuen.jetchiang-ext@solo.io>

docs and fix crd

32aa3b5

Signed-off-by: Jet Chiang <pokyuen.jetchiang-ext@solo.io>

a2a executor

30cd670

Signed-off-by: Jet Chiang <pokyuen.jetchiang-ext@solo.io>

e2e tests for structued output

75e80d3

Signed-off-by: Jet Chiang <pokyuen.jetchiang-ext@solo.io>

ui changes for structured output

cd09123

Signed-off-by: Jet Chiang <pokyuen.jetchiang-ext@solo.io>

supreme-gg-gg added 6 commits September 22, 2026 18:37

fixes

28a00fc

Signed-off-by: Jet Chiang <pokyuen.jetchiang-ext@solo.io>

fix test and lint

1fc6f69

Signed-off-by: Jet Chiang <pokyuen.jetchiang-ext@solo.io>

review comments

16be966

Signed-off-by: Jet Chiang <pokyuen.jetchiang-ext@solo.io>

function cleanup

87adb70

Signed-off-by: Jet Chiang <pokyuen.jetchiang-ext@solo.io>

review comments 2

0adb9f8

Signed-off-by: Jet Chiang <pokyuen.jetchiang-ext@solo.io>

add ConfigMapKeyReference to replace agenttemplate specific type

c1fb364

Signed-off-by: Jet Chiang <pokyuen.jetchiang-ext@solo.io>

supreme-gg-gg force-pushed the jetc/feat/structured-output branch from 1dbd99c to c1fb364 Compare September 22, 2026 22:37

EItanya approved these changes Sep 22, 2026

View reviewed changes

EItanya added this pull request to the merge queue Sep 22, 2026

Merged via the queue into main with commit 4ee8b69 Sep 22, 2026
27 checks passed

EItanya deleted the jetc/feat/structured-output branch September 22, 2026 23:23

Rachael-Graham mentioned this pull request Sep 23, 2026

Docs: write the Structured output page for kagent 1.x kagent-dev/website#518

Closed

8 tasks

Conversation

supreme-gg-gg commented Sep 21, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Summary

Testing

Uh oh!

This comment has been minimized.

supreme-gg-gg commented Sep 22, 2026

Uh oh!

EItanya Sep 22, 2026

Choose a reason for hiding this comment

Uh oh!

supreme-gg-gg Sep 22, 2026

Choose a reason for hiding this comment

Uh oh!

EItanya Sep 22, 2026

Choose a reason for hiding this comment

Uh oh!

supreme-gg-gg Sep 22, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Choose a reason for hiding this comment

Uh oh!

supreme-gg-gg Sep 22, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Charlesthebird left a comment

Choose a reason for hiding this comment

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Charlesthebird left a comment

Choose a reason for hiding this comment

Uh oh!

supreme-gg-gg commented Sep 22, 2026

Uh oh!

moezdil Sep 22, 2026

Choose a reason for hiding this comment

Uh oh!

supreme-gg-gg Sep 22, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Choose a reason for hiding this comment

Uh oh!

moezdil Sep 22, 2026

Choose a reason for hiding this comment

Uh oh!

Uh oh!

Reviewers

Assignees

Labels

Projects

Milestone

Development

Uh oh!

4 participants

supreme-gg-gg commented Sep 21, 2026 •

edited

Loading

supreme-gg-gg Sep 22, 2026 •

edited

Loading

supreme-gg-gg Sep 22, 2026 •

edited

Loading

supreme-gg-gg Sep 22, 2026 •

edited

Loading