GitHub Code Review

Perform code reviews on local changes before pushing, or review open PRs on GitHub. Most of this skill uses plain git — the gh/curl split only matters for PR-level interactions.

Prerequisites

• Authenticated with GitHub (see github-auth skill)
• Inside a git repository

Setup (for PR interactions)

if command -v gh &>/dev/null && gh auth status &>/dev/null; then
  AUTH="gh"
else
  AUTH="git"
  if [ -z "$GITHUB_TOKEN" ]; then
    if [ -f $ENV_FILE ] && grep -q "^GITHUB_TOKEN=" $ENV_FILE; then
      GITHUB_TOKEN=$(grep "^GITHUB_TOKEN=" $ENV_FILE | head -1 | cut -d= -f2 | tr -d '\n\r')
    elif grep -q "github.com" ~/.git-credentials 2>/dev/null; then
      GITHUB_TOKEN=$(grep "github.com" ~/.git-credentials 2>/dev/null | head -1 | sed 's|https://[^:]:\([^@]\)@.*|\1|')
    fi
  fi
fi
REMOTE_URL=$(git remote get-url origin)
OWNER_REPO=$(echo "$REMOTE_URL" | sed -E 's|.*github\.com[:/]||; s|\.git$||')
OWNER=$(echo "$OWNER_REPO" | cut -d/ -f1)
REPO=$(echo "$OWNER_REPO" | cut -d/ -f2)

1. Reviewing Local Changes (Pre-Push)

This is pure git — works everywhere, no API needed.

Get the Diff

# Staged changes (what would be committed)
git diff --staged
All changes vs main (what a PR would contain)

git diff main...HEAD
File names only

git diff main...HEAD --name-only
Stat summary (insertions/deletions per file)

git diff main...HEAD --stat

Review Strategy

• Get the big picture first:

git diff main...HEAD --stat
git log main..HEAD --oneline

• Review file by file — use read_file on changed files for full context, and the diff to see what changed:

git diff main...HEAD -- src/auth/login.py

• Check for common issues:

# Debug statements, TODOs, console.logs left behind
git diff main...HEAD | grep -n "print(\|console\.log\|TODO\|FIXME\|HACK\|XXX\|debugger"
Large files accidentally staged

git diff main...HEAD --stat | sort -t'|' -k2 -rn | head -10
Secrets or credential patterns

git diff main...HEAD | grep -in "password\|secret\|api_key\|token.*=\|private_key"
Merge conflict markers

git diff main...HEAD | grep -n "<<<<<<\|>>>>>>\|======="

• Present structured feedback to the user.

Review Output Format

When reviewing local changes, present findings in this structure:

## Code Review Summary
Critical

src/auth.py:45 — SQL injection: user input passed directly to query.
  Suggestion: Use parameterized queries.
Warnings

src/models/user.py:23 — Password stored in plaintext. Use bcrypt or argon2.
src/api/routes.py:112 — No rate limiting on login endpoint.
Suggestions

src/utils/helpers.py:8 — Duplicates logic in src/core/utils.py:34. Consolidate.
tests/test_auth.py — Missing edge case: expired token test.
Looks Good

Clean separation of concerns in the middleware layer
Good test coverage for the happy path

2. Reviewing a Pull Request on GitHub

View PR Details

With gh:

gh pr view 123
gh pr diff 123
gh pr diff 123 --name-only

With git + curl:

PR_NUMBER=123
Get PR details

curl -s \
  -H "Authorization: token $GITHUB_TOKEN" \
  https://api.github.com/repos/$OWNER/$REPO/pulls/$PR_NUMBER \
  | python3 -c "
import sys, json
pr = json.load(sys.stdin)
print(f\"Title: {pr['title']}\")
print(f\"Author: {pr['user']['login']}\")
print(f\"Branch: {pr['head']['ref']} -> {pr['base']['ref']}\")
print(f\"State: {pr['state']}\")
print(f\"Body:\n{pr['body']}\")"
List changed files

curl -s \
  -H "Authorization: token $GITHUB_TOKEN" \
  https://api.github.com/repos/$OWNER/$REPO/pulls/$PR_NUMBER/files \
  | python3 -c "
import sys, json
for f in json.load(sys.stdin):
    print(f\"{f['status']:10} +{f['additions']:-4} -{f['deletions']:-4}  {f['filename']}\")"

Check Out PR Locally for Full Review

This works with plain git — no gh needed:

# Fetch the PR branch and check it out
git fetch origin pull/123/head:pr-123
git checkout pr-123
Now you can use read_file, search_files, run tests, etc.
View diff against the base branch

git diff main...pr-123

With gh (shortcut):

gh pr checkout 123

Leave Comments on a PR

General PR comment — with gh:

gh pr comment 123 --body "Overall looks good, a few suggestions below."

General PR comment — with curl:

curl -s -X POST \
  -H "Authorization: token $GITHUB_TOKEN" \
  https://api.github.com/repos/$OWNER/$REPO/issues/$PR_NUMBER/comments \
  -d '{"body": "Overall looks good, a few suggestions below."}'

Leave Inline Review Comments

Single inline comment — with gh (via API):

HEAD_SHA=$(gh pr view 123 --json headRefOid --jq '.headRefOid')
gh api repos/$OWNER/$REPO/pulls/123/comments \
  --method POST \
  -f body="This could be simplified with a list comprehension." \
  -f path="src/auth/login.py" \
  -f commit_id="$HEAD_SHA" \
  -f line=45 \
  -f side="RIGHT"

Single inline comment — with curl:

# Get the head commit SHA
HEAD_SHA=$(curl -s \
  -H "Authorization: token $GITHUB_TOKEN" \
  https://api.github.com/repos/$OWNER/$REPO/pulls/$PR_NUMBER \
  | python3 -c "import sys,json; print(json.load(sys.stdin)['head']['sha'])")
curl -s -X POST \
  -H "Authorization: token $GITHUB_TOKEN" \
  https://api.github.com/repos/$OWNER/$REPO/pulls/$PR_NUMBER/comments \
  -d "{
    \"body\": \"This could be simplified with a list comprehension.\",
    \"path\": \"src/auth/login.py\",
    \"commit_id\": \"$HEAD_SHA\",
    \"line\": 45,
    \"side\": \"RIGHT\"
  }"

Submit a Formal Review (Approve / Request Changes)

With gh:

gh pr review 123 --approve --body "LGTM!"
gh pr review 123 --request-changes --body "See inline comments."
gh pr review 123 --comment --body "Some suggestions, nothing blocking."

With curl — multi-comment review submitted atomically:

HEAD_SHA=$(curl -s \
  -H "Authorization: token $GITHUB_TOKEN" \
  https://api.github.com/repos/$OWNER/$REPO/pulls/$PR_NUMBER \
  | python3 -c "import sys,json; print(json.load(sys.stdin)['head']['sha'])")
curl -s -X POST \
  -H "Authorization: token $GITHUB_TOKEN" \
  https://api.github.com/repos/$OWNER/$REPO/pulls/$PR_NUMBER/reviews \
  -d "{
    \"commit_id\": \"$HEAD_SHA\",
    \"event\": \"COMMENT\",
    \"body\": \"Code review from Hermes Agent\",
    \"comments\": [
      {\"path\": \"src/auth.py\", \"line\": 45, \"body\": \"Use parameterized queries to prevent SQL injection.\"},
      {\"path\": \"src/models/user.py\", \"line\": 23, \"body\": \"Hash passwords with bcrypt before storing.\"},
      {\"path\": \"tests/test_auth.py\", \"line\": 1, \"body\": \"Add test for expired token edge case.\"}
    ]
  }"

Event values: "APPROVE", "REQUEST_CHANGES", "COMMENT"

The line field refers to the line number in the new version of the file. For deleted lines, use "side": "LEFT".

3. Review Checklist

When performing a code review (local or PR), systematically check:

Correctness

• Does the code do what it claims?
• Edge cases handled (empty inputs, nulls, large data, concurrent access)?
• Error paths handled gracefully?

Security

• No hardcoded secrets, credentials, or API keys
• Input validation on user-facing inputs
• No SQL injection, XSS, or path traversal
• Auth/authz checks where needed

Code Quality

• Clear naming (variables, functions, classes)
• No unnecessary complexity or premature abstraction
• DRY — no duplicated logic that should be extracted
• Functions are focused (single responsibility)

Testing

• New code paths tested?
• Happy path and error cases covered?
• Tests readable and maintainable?

Performance

• No N+1 queries or unnecessary loops
• Appropriate caching where beneficial
• No blocking operations in async code paths

Documentation

• Public APIs documented
• Non-obvious logic has comments explaining "why"
• README updated if behavior changed

4. Pre-Push Review Workflow

When the user asks you to "review the code" or "check before pushing":

• git diff main...HEAD --stat — see scope of changes
• git diff main...HEAD — read the full diff
• For each changed file, use read_file if you need more context
• Apply the checklist above
• Present findings in the structured format (Critical / Warnings / Suggestions / Looks Good)
• If critical issues found, offer to fix them before the user pushes

5. PR Review Workflow (End-to-End)

When the user asks you to "review PR #N", "look at this PR", or gives you a PR URL, follow this recipe:

Step 1: Set up environment

source skills/github/github-auth/scripts/gh-env.sh
Or run the inline setup block from the top of this skill

Step 2: Gather PR context

Get the PR metadata, description, and list of changed files to understand scope before diving into code.

With gh:

gh pr view 123
gh pr diff 123 --name-only
gh pr checks 123

With curl:

PR_NUMBER=123
PR details (title, author, description, branch)

curl -s -H "Authorization: token $GITHUB_TOKEN" \
  https://api.github.com/repos/$GH_OWNER/$GH_REPO/pulls/$PR_NUMBER
Changed files with line counts

curl -s -H "Authorization: token $GITHUB_TOKEN" \
  https://api.github.com/repos/$GH_OWNER/$GH_REPO/pulls/$PR_NUMBER/files

Step 3: Check out the PR locally

This gives you full access to read_file, search_files, and the ability to run tests.

git fetch origin pull/$PR_NUMBER/head:pr-$PR_NUMBER
git checkout pr-$PR_NUMBER

Step 4: Read the diff and understand changes

# Full diff against the base branch
git diff main...HEAD
Or file-by-file for large PRs

git diff main...HEAD --name-only
Then for each file:

git diff main...HEAD -- path/to/file.py

For each changed file, use read_file to see full context around the changes — diffs alone can miss issues visible only with surrounding code.

Step 5: Run automated checks locally (if applicable)

# Run tests if there's a test suite
python -m pytest 2>&1 | tail -20
or: npm test, cargo test, go test ./..., etc.
Run linter if configured

ruff check . 2>&1 | head -30
or: eslint, clippy, etc.

Step 6: Apply the review checklist (Section 3)

Go through each category: Correctness, Security, Code Quality, Testing, Performance, Documentation.

Step 7: Post the review to GitHub

Collect your findings and submit them as a formal review with inline comments.

With gh:

# If no issues — approve
gh pr review $PR_NUMBER --approve --body "Reviewed by Hermes Agent. Code looks clean — good test coverage, no security concerns."
If issues found — request changes with inline comments

gh pr review $PR_NUMBER --request-changes --body "Found a few issues — see inline comments."

With curl — atomic review with multiple inline comments:

HEAD_SHA=$(curl -s -H "Authorization: token $GITHUB_TOKEN" \
  https://api.github.com/repos/$GH_OWNER/$GH_REPO/pulls/$PR_NUMBER \
  | python3 -c "import sys,json; print(json.load(sys.stdin)['head']['sha'])")
Build the review JSON — event is APPROVE, REQUEST_CHANGES, or COMMENT

curl -s -X POST \
  -H "Authorization: token $GITHUB_TOKEN" \
  https://api.github.com/repos/$GH_OWNER/$GH_REPO/pulls/$PR_NUMBER/reviews \
  -d "{
    \"commit_id\": \"$HEAD_SHA\",
    \"event\": \"REQUEST_CHANGES\",
    \"body\": \"## Hermes Agent Review\n\nFound 2 issues, 1 suggestion. See inline comments.\",
    \"comments\": [
      {\"path\": \"src/auth.py\", \"line\": 45, \"body\": \"🔴 Critical: User input passed directly to SQL query — use parameterized queries.\"},
      {\"path\": \"src/models.py\", \"line\": 23, \"body\": \"⚠️ Warning: Password stored without hashing.\"},
      {\"path\": \"src/utils.py\", \"line\": 8, \"body\": \"💡 Suggestion: This duplicates logic in core/utils.py:34.\"}
    ]
  }"

Step 8: Also post a summary comment

In addition to inline comments, leave a top-level summary so the PR author gets the full picture at a glance. Use the review output format from references/review-output-template.md.

With gh:

gh pr comment $PR_NUMBER --body "$(cat <<'EOF'
Code Review Summary
Verdict: Changes Requested (2 issues, 1 suggestion)
🔴 Critical

src/auth.py:45 — SQL injection vulnerability
⚠️ Warnings

src/models.py:23 — Plaintext password storage
💡 Suggestions

src/utils.py:8 — Duplicated logic, consider consolidating
✅ Looks Good

Clean API design
Good error handling in the middleware layer

Reviewed by Hermes Agent
EOF
)"

Step 9: Clean up

git checkout main
git branch -D pr-$PR_NUMBER

Decision: Approve vs Request Changes vs Comment

• Approve — no critical or warning-level issues, only minor suggestions or all clear
• Request Changes — any critical or warning-level issue that should be fixed before merge
• Comment — observations and suggestions, but nothing blocking (use when you're unsure or the PR is a draft)