diff-fox

DiffFox

AI-powered code review with 6 specialized agents. Runs as a GitHub Action on PRs or as a Claude Code plugin locally.

What It Does

DiffFox analyzes code changes from 6 engineering perspectives simultaneously:

| Agent | Focus | |-------|-------| | Logic | Bugs at runtime — null handling, off-by-one, incorrect conditions, edge cases | | Security | Injection, auth bypass, secrets, XSS, SSRF, data exposure | | Architecture | Design violations, DRY, API contracts, coupling, tech debt | | Performance | N+1 queries, O(n^2) algorithms, blocking I/O, resource leaks | | Risk | Blast radius, backwards compatibility, migration safety, rollback | | COGS | Unbounded queries, LLM calls in loops, missing rate limits, cost spikes |

Each agent has its own exclusion rules and precedent rules to minimize false positives. Findings are verified by a second-opinion LLM pass, deduplicated across agents, and validated against diff lines before posting.

Quick Start

GitHub Action

# .github/workflows/diff-fox.yml
name: DiffFox Review
on:
  pull_request:
    types: [opened, synchronize, ready_for_review]

jobs:
  review:
    runs-on: ubuntu-latest
    permissions:
      pull-requests: write
      contents: read
    steps:
      - uses: actions/checkout@v6
        with:
          fetch-depth: 0
      - uses: mthooyavan/diff-fox@main
        with:
          anthropic-api-key: ${{ secrets.ANTHROPIC_API_KEY }}

> Dependabot PRs: If you use Dependabot, add ANTHROPIC_API_KEY under Settings > Secrets > Dependabot separately — Dependabot can't access regular repo secrets. Alternatively, skip DiffFox for Dependabot by adding if: github.actor != 'dependabot[bot]' to the job.

Claude Code Plugin

Install from GitHub (inside any Claude Code session):

/plugin marketplace add mthooyavan/diff-fox
/plugin install diff-fox@diff-fox-marketplace

Or install from local clone:

git clone https://github.com/mthooyavan/diff-fox.git ~/diff-fox

Then in Claude Code:

/plugin marketplace add ~/diff-fox
/plugin install diff-fox@diff-fox-marketplace

Usage (start a new Claude Code session after install):

/diff-fox              # Review all changes on current branch vs main/master
/diff-fox-pr 123       # Review a specific GitHub PR

No Python dependencies — uses Claude Code's built-in Read, Grep, Glob, and Bash tools.

> Note: If you also have the code-review plugin installed, use /diff-fox (not /review) to avoid name collision.

Configuration

Create .diff-fox/config.yml in your repo root:

# Enable/disable agents
agents:
  logic: true
  security: true
  architecture: true
  performance: true
  risk: true
  cogs: true

  # Per-agent file filtering
  security:
    enabled: true
    include: ["src/api/**"]
    skip: ["src/api/tests/**"]

# Custom guidelines injected into agent prompts
guidelines:
  security:
    - "All API endpoints must validate JWT tokens"
  architecture:
    - "Database access only through repository pattern"

# Global file filtering
skip:
  - "src/generated/**"
  - "**/*.min.js"
  - "vendor/**"

# Suppress findings matching these title patterns
suppress_filters:
  - "commented-out code"

# Optional: Jira integration
jira:
  enabled: true

The config supports hierarchical merging — repo-level config is merged with project-level config found by walking up from the primary changed directory.

Action Inputs

| Input | Required | Default | Description | |-------|----------|---------|-------------| | anthropic-api-key | Yes | — | Anthropic API key | | model | No | claude-sonnet-4-6-20250514 | Claude model to use | | config-path | No | .diff-fox/config.yml | Config file path | | jira-mcp-url | No | — | Jira MCP server URL | | jira-enabled | No | false | Enable Jira context | | post-comments | No | true | Post comments to PR |

How It Works

PR opened
  → Fetch diff + existing comments
  → Load .diff-fox/config.yml
  → Context enrichment (symbol extraction, call graphs, impact analysis)
  → 6 agents review in parallel
  → Verification (second-opinion LLM pass)
  → Hard security exclusion filter (regex)
  → Semantic dedup (LLM merges cross-agent duplicates)
  → Validate against diff lines
  → Filter already-posted comments
  → Jira alignment check (optional)
  → Post inline comments + summary

Deterministic vs AI-Powered

Deterministic (no LLM):

• Diff parsing, symbol extraction (Python AST + regex for other languages)
• Call site search, callee extraction, impact analysis
• Security hard exclusion filter (compiled regex patterns)
• Diff line validation, heuristic dedup, severity ranking, formatting

AI-Powered (Claude):

• 6 parallel agent reviews with specialized prompts
• Finding verification (second opinion)
• Semantic dedup (cross-agent/cross-file merge)
• Jira alignment check

Architecture

diff-fox/
├── action/              # GitHub Action (Docker-based)
│   ├── action.yml
│   ├── Dockerfile
│   └── entrypoint.py
├── plugin/              # Claude Code Plugin
│   ├── plugin.json
│   ├── agents/reviewer.md
│   └── skills/
├── src/diff_fox/        # Core library
│   ├── config/          # .diff-fox/config.yml loader
│   ├── context/         # Symbol extraction, call graphs, impact
│   ├── review/          # Pipeline, verification, dedup, agents
│   ├── scm/             # GitHub API client
│   ├── integrations/    # Jira MCP
│   ├── output/          # GitHub poster, text formatter
│   ├── llm.py           # Anthropic SDK wrapper
│   └── run_review.py    # Main orchestrator
└── pyproject.toml

Dependencies

• anthropic — Claude API
• httpx — GitHub API client
• pyyaml — Config parsing
• pydantic — Data models

No LangChain. No LangGraph. No FastAPI. No Temporal. No database.

License

MIT