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.

When to Use

Use this skill when you need to:

• Review local uncommitted changes before pushing to a remote branch
• Perform a structured code review on an open GitHub pull request
• Leave inline comments on specific lines of a PR diff
• Submit a formal PR review (Approve, Request Changes, or Comment)
• Check for common issues (security flaws, debug leftovers, merge conflicts) before merging
• Audit a large PR systematically with a checklist-based approach

Don't use for:

• Non-GitHub repositories (GitLab, Bitbucket — the API calls and URL structures differ)
• Simple typo fixes or one-line formatting changes (just fix and commit directly)
• Reviewing dependency-only or lockfile-only diffs (use dedicated diff inspection tools)
• Code style enforcement (use a linter like ruff, eslint, or clippy instead)

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 "$GITHUB_TOKEN" ]; then
    if _hermes_env="${HERMES_HOME:-$HOME/.hermes}/.env"; [ -f "$_hermes_env" ] && grep -q "^GITHUB_TOKEN=" "$_hermes_env"; then
      GITHUB_TOKEN=$(grep "^GITHUB_TOKEN=" "$_hermes_env" | head -1 | cut -d= -f2 | tr -d '\n\r')
    elif grep -q "github.com" ~/.git-credentials 2>/dev/null; then
      GITHUB_TOKEN=$(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

1. Get the big picture first:

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

2. 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

3. 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 "<<<<<<\|>>>>>>\|======="

4. 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":

1. git diff main...HEAD --stat — see scope of changes
2. git diff main...HEAD — read the full diff
3. For each changed file, use read_file if you need more context
4. Apply the checklist above
5. Present findings in the structured format (Critical / Warnings / Suggestions / Looks Good)
6. 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 "${HERMES_HOME:-$HOME/.hermes}/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)

---

Pitfalls

• Token exposure: The curl examples use *** as a placeholder. Never hardcode tokens in scripts — use environment variables ($GITHUB_TOKEN) or gh auth for secure authentication.
• Diff complexity: Large diffs (>500 lines) are hard to review as one blob. Break into file-by-file reviews using git diff main...HEAD -- path/to/file.py.
• Commit SHA mismatch: Inline comments require the correct head commit SHA. If the PR receives new commits after you fetch the SHA, your comments may be attached to the wrong line or rejected entirely.
• Review vs Comment confusion: A formal review (gh pr review --approve) is different from a general comment (gh pr comment). Reviews can block merging; comments cannot.
• Line number reference errors: The line field in review comments refers to the line number in the new (or old) version of the file. For deleted lines, use "side": "LEFT". Wrong side/line values produce malformed comments.
• Permission denied: You need write access to the repository to submit reviews on a PR. Read-only access allows viewing but not commenting.
• Branch cleanup: Forgetting to delete local review branches (pr-123) creates clutter over time. Clean up with git branch -D pr-123 after each review.
• Review fatigue: Checking every line of a 2000-line PR is error-prone and misses issues. Use --stat and --name-only first to scope the review, then prioritize high-risk files (security, auth, data handling, input validation).
• Fetched PR branch goes stale: After fetching a PR branch, the PR author may push new commits. Re-fetch (git fetch origin pull/N/head:pr-N) to get the latest diff before leaving comments.
• Missing context: Diffs show what changed, not the surrounding code. Always read_file on the full file to understand the context around each change.

Verification

Before marking a code review as complete:

Local Changes Review

• git diff main...HEAD --stat reviewed to understand scope
• Full diff inspected for correctness and logic errors
• Security scan performed (secrets, SQL injection, XSS, path traversal)
• Debug artifacts checked (print(), console.log, TODO, FIXME, debugger)
• Merge conflict markers (<<<<<<<, >>>>>>, =======) absent
• Findings presented in structured format (Critical / Warnings / Suggestions / Looks Good)

PR Review

• PR title, description, and scope fully understood
• All changed files reviewed (not just a subset)
• Inline comments reference the correct lines and head commit SHA
• Formal review submitted with appropriate event (Approve / Request Changes / Comment)
• Summary comment posted with an overall verdict
• Local PR branch cleaned up (git branch -D pr-N)
• All CI checks passing (if the PR has checks configured)
• No critical or security issues remain unresolved