diff --git a/.pre-commit-config.yaml b/.pre-commit-config.yaml
index c640cf003..f972a2c97 100644
--- a/.pre-commit-config.yaml
+++ b/.pre-commit-config.yaml
@@ -30,6 +30,11 @@ repos:
         types: [python]
         pass_filenames: false
         args: [src/adcp]
+      - id: check-commit-msg
+        name: release-please commit subject check
+        entry: scripts/check-commit-msg.sh
+        language: script
+        stages: [commit-msg]
 
   # Security scanning with bandit
   - repo: https://github.com/PyCQA/bandit
diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
index a443d8369..ff1e3051e 100644
--- a/CONTRIBUTING.md
+++ b/CONTRIBUTING.md
@@ -10,9 +10,11 @@ git clone https://github.com/adcontextprotocol/adcp-client-python.git
 cd adcp-client-python
 ```
 
-2. Install dependencies:
+2. Install dependencies and pre-commit hooks:
 ```bash
 pip install -e ".[dev]"
+pre-commit install
+pre-commit install --hook-type commit-msg
 ```
 
 3. Run tests:
@@ -82,6 +84,40 @@ src/adcp/
 4. Update documentation
 5. Submit PR with clear description
 
+### PR Title Format
+
+This repository uses squash merges. The PR title becomes the commit subject that
+release-please reads to build the CHANGELOG and determine version bumps.
+
+**The description portion of the commit subject — the text after `type(scope):` —
+must not contain `(`, `)`, or `"` characters.** The release-please parser treats
+those characters as grammar tokens when they appear in the description and silently
+drops the commit from the CHANGELOG with no error signal. (The `type(scope)` prefix
+itself is fine; only the description portion is constrained.)
+
+**Wrong — parser drops these commits silently:**
+
+```
+fix(auth): synthesize AuthInfo(kind="bearer") in _build_request_context
+feat(auth): serve(auth=BearerTokenAuth(...)) — A2A sibling shortcut
+```
+
+**Right — move code examples and parenthetical details to the PR body:**
+
+```
+fix(auth): synthesize bearer AuthInfo in _build_request_context
+feat(auth): add A2A sibling and cross-transport shortcut for bearer auth
+```
+
+Place code snippets, type names with parens, and parenthetical clarifications in the PR
+body (release-please reads body footers like `BREAKING CHANGE:` and `Fixes #N` but
+otherwise ignores the body for CHANGELOG purposes).
+
+A `commit-msg` pre-commit hook (`scripts/check-commit-msg.sh`) catches violations on
+direct commits. It does **not** catch squash-merge subjects (those are set by GitHub on
+merge from the PR title), so keeping the PR title clean is the primary responsibility.
+Hook setup is included in step 2 of Development Setup above.
+
 ## Questions?
 
 Open an issue or email maintainers@adcontextprotocol.org
diff --git a/scripts/check-commit-msg.sh b/scripts/check-commit-msg.sh
new file mode 100755
index 000000000..5507732ca
--- /dev/null
+++ b/scripts/check-commit-msg.sh
@@ -0,0 +1,38 @@
+#!/usr/bin/env bash
+# Validates commit subjects against release-please parser constraints.
+# Embedded ( ) or " in the description silently drop commits from the CHANGELOG.
+# NOTE: this hook runs on direct commits only — squash-merge subjects (set by
+# GitHub from the PR title) bypass it. Keep the PR title clean as the primary fix.
+#
+# Enable: pre-commit install --hook-type commit-msg
+
+set -euo pipefail
+
+msg_file="$1"
+subject=$(head -1 "$msg_file")
+
+# Only validate conventional commit messages: type(scope): desc or type: desc
+cc_pattern='^[a-z]+(\([^)]*\))?(!)?: '
+if echo "$subject" | grep -qE "$cc_pattern"; then
+    description="${subject#*: }"
+    if echo "$description" | grep -qE '[()"]'; then
+        echo ""
+        echo "commit-msg: release-please will silently drop this commit from the CHANGELOG."
+        echo ""
+        echo "  Subject: $subject"
+        echo ""
+        echo '  The description (text after "type(scope):") contains ( ) or " characters,'
+        echo "  which break release-please's conventional commit parser."
+        echo ""
+        echo "  Fix: reword to avoid parentheses and quotes in the description."
+        echo "  Move code snippets and type names with parens to the PR body instead."
+        echo ""
+        echo "  Example:"
+        echo '    Wrong: fix(auth): synthesize AuthInfo(kind="bearer") in _build_request_context'
+        echo "    Right: fix(auth): synthesize bearer AuthInfo in _build_request_context"
+        echo ""
+        exit 1
+    fi
+fi
+
+exit 0