coderace 0.3.0

Race coding agents against each other on real tasks

coderace

Stop reading blog comparisons. Race coding agents against each other on real tasks in your repo with your code.

Every week there's a new "Claude Code vs Codex vs Cursor" post. They test on toy problems with cherry-picked examples. coderace gives you automated, reproducible, scored comparisons on the tasks you actually care about.

Define a task. Run it against Claude Code, Codex, Aider, Gemini CLI, and OpenCode. Get a scored comparison table.

Install

pip install coderace

Quick Start

# Create a task template
coderace init fix-auth-bug

# Edit the task file (describe the bug, set test command)
# Then race the agents:
coderace run fix-auth-bug.yaml

# Or race them in parallel (uses git worktrees):
coderace run fix-auth-bug.yaml --parallel

# View results from the last run
coderace results fix-auth-bug.yaml

coderace diff — Race Agents on a Real PR Diff

Turn any git diff into a coderace task with one command:

# Race agents to review the latest commit
git diff HEAD~1 | coderace diff --mode review | coderace run /dev/stdin

# Generate a task YAML from a patch file, then run it
git diff main...my-branch > my-pr.patch
coderace diff --file my-pr.patch --mode fix --output task.yaml
coderace run task.yaml

Modes

Mode	What agents are asked to do
review	Review the changes and provide feedback on correctness, style, and potential issues
fix	Fix bugs or problems introduced by the diff
improve	Enhance performance, readability, or robustness of the changed code

Flags

--file PATH       Read diff from file instead of stdin
--mode TEXT       review | fix | improve  (default: review)
--agents TEXT     Override agent list (repeatable: --agents claude --agents aider)
--name TEXT       Task name in generated YAML  (default: diff-task)
--output PATH     Write YAML to file instead of stdout
--test-command    Test command to embed in the task (default: pytest tests/ -x)
--lint-command    Lint command to embed in the task (default: ruff check .)

Task Format

name: fix-auth-bug
description: |
  The login endpoint returns 500 when email contains a plus sign.
  Fix the email validation in auth/validators.py.
repo: .
test_command: pytest tests/test_auth.py -x
lint_command: ruff check .
timeout: 300
agents:
  - claude
  - codex
  - aider

What It Does

For each agent in the task:

1. Creates a fresh git branch (coderace/<agent>-<task>)
2. Invokes the agent CLI with the task description
3. Runs your test command
4. Runs your lint command (optional)
5. Computes a composite score

Scoring

Metric	Weight	Description
Tests pass	40%	Did the test command exit 0?
Exit clean	20%	Did the agent itself exit 0 without timeout?
Lint clean	15%	Did the lint command exit 0?
Wall time	15%	Faster is better (normalized across agents)
Lines changed	10%	Fewer is better (normalized across agents)

Output

Terminal table with Rich formatting:

┌──────┬────────┬───────┬───────┬──────┬──────┬──────────┬───────┐
│ Rank │ Agent  │ Score │ Tests │ Exit │ Lint │ Time (s) │ Lines │
├──────┼────────┼───────┼───────┼──────┼──────┼──────────┼───────┤
│  1   │ claude │  85.0 │ PASS  │ PASS │ PASS │     10.5 │    42 │
│  2   │ codex  │  70.0 │ PASS  │ PASS │ FAIL │     15.2 │    98 │
│  3   │ aider  │  55.0 │ FAIL  │ PASS │ PASS │      8.1 │    31 │
└──────┴────────┴───────┴───────┴──────┴──────┴──────────┴───────┘

Results also saved as JSON in .coderace/<task>-results.json and as a self-contained HTML report in .coderace/<task>-results.html.

Try It Now

The examples/ directory has ready-to-use task templates:

# Race agents on adding type hints to your project
coderace run examples/add-type-hints.yaml

# Race agents on fixing an edge case bug
coderace run examples/fix-edge-case.yaml

# Race agents on writing new tests
coderace run examples/write-tests.yaml

Edit the repo and description fields to point at your actual project and describe your real task.

Statistical Mode

Run each agent multiple times and get mean ± stddev:

coderace run task.yaml --runs 5

Useful for tasks with variable outcomes (LLM nondeterminism is real).

HTML Reports

Export results as a shareable single-file HTML report:

# Auto-generated on every run at .coderace/<task>-results.html
# Or export manually:
coderace results task.yaml --html report.html

The HTML report has sortable columns and a dark theme. Drop it in a blog post or Slack.

Custom Scoring

Override the default weights in your task YAML:

scoring:
  tests: 60   # tests passing (default 40)
  exit: 20    # clean exit (default 20)
  lint: 10    # lint clean (default 15)
  time: 5     # wall time (default 15)
  lines: 5    # lines changed (default 10)

Weights are normalized automatically (don't need to sum to 100).

Supported Agents

Agent	CLI	Notes
Claude Code	claude	Anthropic's coding agent
Codex	codex	OpenAI Codex CLI
Aider	aider	Git-integrated AI coding
Gemini CLI	gemini	Google's Gemini CLI
OpenCode	opencode	Open-source terminal agent

Each agent must be installed and authenticated separately.

Parallel Mode

Use --parallel (or -p) to run all agents simultaneously using git worktrees. Each agent gets its own isolated working directory, so they don't interfere with each other.

coderace run task.yaml --parallel

Sequential mode (default) runs agents one at a time on the same repo.

Why coderace?

Blog posts compare models. coderace compares agents on your work.

• Run on your actual codebase, not HumanEval
• Automated scoring: tests, lint, time, lines changed
• Parallel mode with git worktrees (no interference between agents)
• JSON output for CI integration and tracking over time
• Works with any agent that has a CLI

The goal isn't "which model is best." It's "which agent solves my specific problem best."

CI Integration

Use coderace in GitHub Actions to automatically race agents on PRs and post results as comments.

Quick setup

1. Copy examples/ci-race-on-pr.yml into .github/workflows/ in your repo.
2. Create a task YAML at .github/coderace-task.yaml (see Task Format).
3. Install the agent CLIs your task requires (see comments in the workflow file).
4. Open or update a PR — results appear as a PR comment automatically.

Workflow: Race on every PR

name: Race Coding Agents

on:
  pull_request:
    branches: [main]

jobs:
  race:
    runs-on: ubuntu-latest
    permissions:
      contents: read
      pull-requests: write

    steps:
      - uses: actions/checkout@v4

      - name: Run coderace
        uses: mikiships/coderace@v0.3
        with:
          task: .github/coderace-task.yaml
          agents: claude,aider
          github-token: ${{ secrets.GITHUB_TOKEN }}

Workflow: Race only when "race-agents" label is added

Cost-control pattern: only race when a maintainer deliberately triggers it.

name: Race Coding Agents (on label)

on:
  pull_request:
    types: [labeled]

jobs:
  race:
    if: github.event.label.name == 'race-agents'
    runs-on: ubuntu-latest
    permissions:
      contents: read
      pull-requests: write

    steps:
      - uses: actions/checkout@v4

      - name: Run coderace
        uses: mikiships/coderace@v0.3
        with:
          task: .github/coderace-task.yaml
          github-token: ${{ secrets.GITHUB_TOKEN }}

Action inputs

Input	Description	Default
task	Path to coderace task YAML	(required)
agents	Comma-separated agents to race	(from task file)
parallel	Run agents in parallel (true/false)	false
github-token	Token for posting PR comments	${{ github.token }}
coderace-version	coderace version to install	latest
python-version	Python version	3.11

Example PR comment

The action automatically posts (and updates on re-run) a comment like:

✅ coderace — fix-auth-bug | Winner: claude (85.0 pts) | 3 agent(s) raced

Rank	Agent	Score	Tests	Lint	Exit	Time (s)	Lines
1	claude	85.0	✅	✅	✅	10.5	42
2	codex	70.0	✅	❌	✅	15.2	98
3	aider	55.0	❌	✅	✅	8.1	31

The action uses a hidden HTML marker to find and update existing comments, so re-running doesn't spam the PR.

See Also

• pytest-agentcontract -- Deterministic CI tests for LLM agent trajectories. Record once, replay offline, assert contracts. Pairs well with coderace: race agents to find the best one, then lock down its behavior with contract tests.

Requirements

• Python 3.10+
• Git
• At least one coding agent CLI installed

License

MIT