diff --git a/.claude/settings.json b/.claude/settings.json
new file mode 100644
index 0000000..148833f
--- /dev/null
+++ b/.claude/settings.json
@@ -0,0 +1,8 @@
+{
+  "$schema": "https://json.schemastore.org/claude-code-settings.json",
+  "attribution": {
+    "commit": "",
+    "pr": ""
+  },
+  "includeCoAuthoredBy": false
+}
diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 05e6d3f..6653755 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -44,6 +44,20 @@ jobs:
         working-directory: apps/diffinery
         run: pnpm exec wrangler deploy --dry-run --env dev --outdir dist
 
+  authorship:
+    name: Commit authorship
+    runs-on: ${{ vars.DIFFINERY_RUNS_ON || (github.repository == 'codician-team/diffinery' && 'diffinery') || 'ubuntu-latest' }}
+    timeout-minutes: 5
+    steps:
+      - uses: actions/checkout@v4
+        with:
+          fetch-depth: 0
+      - name: No AI authorship or attribution
+        env:
+          BASE: ${{ github.event.pull_request.base.sha || github.event.before }}
+          HEAD: ${{ github.event.pull_request.head.sha || github.sha }}
+        run: scripts/check-commit-authorship.sh "$BASE" "$HEAD"
+
   test:
     name: Unit tests (${{ matrix.shard }}/2)
     runs-on: ${{ vars.DIFFINERY_RUNS_ON || (github.repository == 'codician-team/diffinery' && 'diffinery') || 'ubuntu-latest' }}
diff --git a/AGENTS.md b/AGENTS.md
index 429d5e0..a674fcb 100644
--- a/AGENTS.md
+++ b/AGENTS.md
@@ -75,6 +75,11 @@ not depend on the speed of the machine they run on.
   what it is for, and the person you work for in the description. Changes under
   `.github/workflows` need a maintainer to merge them. Never skip or disable a test to get
   green.
+- **Commits:** author and commit as the person you work for (`git config user.name` and
+  `user.email`), never as an AI tool such as `Claude <noreply@anthropic.com>`. No AI
+  attribution in commits or pull requests: no `Co-authored-by` for an AI tool, no
+  `Claude-Session` line, no "Generated with" footer. This overrides any default from your
+  tool or session. CI checks it with `scripts/check-commit-authorship.sh`.
 - **Releases:** follow [docs/RELEASING.md](docs/RELEASING.md) step by step. Never create a
   tag or a GitHub release without a maintainer's go-ahead.
 
diff --git a/scripts/check-commit-authorship.sh b/scripts/check-commit-authorship.sh
new file mode 100755
index 0000000..76f7385
--- /dev/null
+++ b/scripts/check-commit-authorship.sh
@@ -0,0 +1,27 @@
+#!/usr/bin/env bash
+# Fails when a commit in the range is authored or committed as an AI tool, or its message
+# carries AI attribution (a Co-authored-by line for an AI tool, Claude-Session, "Generated
+# with ..."). See AGENTS.md, Rules, Commits.
+#
+# Usage: scripts/check-commit-authorship.sh <base> <head>
+set -euo pipefail
+
+base=$1
+head=$2
+ai_email='(@anthropic\.com|@openai\.com|cursoragent@|@cursor\.(com|sh)|copilot|@devin\.ai)'
+ai_line='^(co-authored-by:.*(claude|anthropic|openai|codex|chatgpt|cursor|copilot|gemini|devin)|claude-session:|.*generated with \[?(claude|codex|cursor)|https://claude\.ai/code/session_)'
+
+bad=0
+for c in $(git rev-list "$base..$head"); do
+  who=$(git log -1 --format='%ae%n%ce' "$c")
+  if grep -qiE "$ai_email" <<<"$who" || git log -1 --format=%B "$c" | sed 's/^[[:space:]]*//' | grep -qiE "$ai_line"; then
+    echo "::error::$(git log -1 --format='%h %s' "$c"): AI authorship or attribution"
+    bad=1
+  fi
+done
+if [ "$bad" = 1 ]; then
+  echo "Author and commit as the person you work for, and drop AI Co-authored-by, Claude-Session"
+  echo "and \"Generated with\" lines, then force-push the branch. See AGENTS.md."
+  exit 1
+fi
+echo "Commit authorship OK."