GitHub Code Review with Hermes Agent: Local Diffs, PRs, and Inline Comments

The GitHub Code Review skill lets you review local changes before pushing and inspect open pull requests on GitHub. It uses plain git for local diffs and either the gh CLI or curl against the GitHub REST API for PR interactions. You would reach for this when you want an automated agent to audit code changes, catch common issues, and post structured feedback directly on a PR.

What it does

This skill gives Hermes Agent the ability to:

• Show staged or unstaged diffs against a base branch (typically main).
• List changed files, insertion/deletion counts, and commit summaries.
• Scan diffs for debug statements, TODO markers, secrets, and merge conflict markers.
• Fetch PR metadata, changed files, and the full diff from GitHub.
• Check out a PR branch locally for deeper inspection with read_file and search_files.
• Leave general PR comments, inline review comments, and submit formal reviews (approve, request changes, or comment).
• Follow a structured review checklist covering correctness, security, code quality, testing, performance, and documentation.
• Present findings in a consistent format (Critical / Warnings / Suggestions / Looks Good).

Before you start

• You must be authenticated with GitHub. The github-auth skill handles this. The setup block at the top of this skill tries gh auth status first; if that fails, it falls back to GITHUB_TOKEN from the environment, from $HERMES_HOME/.env, or from ~/.git-credentials.
• You must be inside a git repository that has a remote named origin pointing to a GitHub URL. The skill parses OWNER and REPO from that remote.
• The skill works on Linux, macOS, and Windows.
• For PR interactions, you need either the gh CLI installed and authenticated, or a GITHUB_TOKEN with appropriate repo scope.

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

1. 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

1. 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 "<<<<<<\|>>>>>>\|======="

1. 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)

When not to use it

This skill is designed for reviewing code changes in a GitHub repository. It is not a substitute for a human code review that requires deep domain knowledge or architectural judgment. If the PR involves complex business logic, security-sensitive cryptographic code, or decisions that require product context, you should still involve a human reviewer. The skill also cannot run the application or verify runtime behavior beyond what tests and static analysis can show.

Limits and gotchas

• The line field in inline comments refers to the line number in the new version of the file. For deleted lines, you must set "side": "LEFT".
• The skill relies on the gh CLI or a GITHUB_TOKEN with appropriate permissions. If neither is configured, PR interactions will fail.
• The setup block parses OWNER and REPO from the origin remote URL. If your remote uses a different name or format, you may need to adjust the parsing.
• The pre-push review workflow assumes main as the base branch. If your project uses a different default branch, replace main accordingly.
• The skill does not handle GitHub Enterprise instances out of the box; the API endpoint would need to be changed.

Related skills

• github-auth, handles authentication setup that this skill depends on.
• github-pr-workflow, a higher-level skill that may orchestrate PR creation, merging, and other operations alongside review.