diff --git a/action.yml b/action.yml
index e5e4231..27df515 100644
--- a/action.yml
+++ b/action.yml
@@ -37,6 +37,10 @@ inputs:
     description: "Max diff size in bytes before truncation (0 = unlimited)"
     required: false
     default: "80000"
+  debug:
+    description: "Include agent tool log in the review comment (shows which files were read)"
+    required: false
+    default: "false"
 
 runs:
   using: "docker"
diff --git a/entrypoint.sh b/entrypoint.sh
index 35336c8..e5589de 100755
--- a/entrypoint.sh
+++ b/entrypoint.sh
@@ -16,6 +16,7 @@ export PI_REVIEW_PROMPT="${INPUT_REVIEW_PROMPT:-}"
 export PI_EXCLUDE="${INPUT_EXCLUDE_PATTERNS:-*.lock package-lock.json yarn.lock pnpm-lock.yaml *.min.js *.min.css *.map}"
 export PI_MAX_DIFF="${INPUT_MAX_DIFF_BYTES:-80000}"
 export PI_TOKEN="${INPUT_TOKEN}"
+export PI_DEBUG="${INPUT_DEBUG:-false}"
 
 # The calling repo is mounted at GITHUB_WORKSPACE by both GitHub and Gitea.
 # cd into it so git commands work against the right repo.
diff --git a/scripts/review.sh b/scripts/review.sh
index 9237c99..43ebb64 100755
--- a/scripts/review.sh
+++ b/scripts/review.sh
@@ -125,18 +125,40 @@ PROMPT="${PROMPT}
 The git diff is at /tmp/pi-diff.txt. Start by reading it, then read any files you need for full context."
 
 # Run Pi in print mode (non-interactive, no session persistence)
+# Capture stderr (tool call log) always — only show it when debug is on
 pi --no-session \
   ${PROVIDER_FLAG} \
   --model "${PI_MODEL}" \
   --tools "${PI_TOOLS}" \
   -p "${PROMPT}" \
-  > /tmp/pi-review.md 2>/dev/null
+  > /tmp/pi-review.md 2>/tmp/pi-agent.log
 
 if [ ! -s /tmp/pi-review.md ]; then
   echo "::error::Pi generated no output"
+  echo "Agent log (last 30 lines):"
+  tail -30 /tmp/pi-agent.log
   exit 1
 fi
 
+# If debug mode, append the agent's tool log to the review
+if [ "${PI_DEBUG}" = "true" ]; then
+  AGENT_LOG=$(sed 's/\x1b\[[0-9;]*m//g' /tmp/pi-agent.log | head -200)
+  cat >> /tmp/pi-review.md << LOGEOF
+
+---
+
+<details>
+<summary>🔍 <strong>Agent Tool Log</strong> (debug)</summary>
+
+\`\`\`
+${AGENT_LOG}
+\`\`\`
+
+</details>
+LOGEOF
+  echo "Debug: agent log appended to review"
+fi
+
 echo "Review generated successfully."
 echo "::endgroup::"