agenttester 0.5.2

Run a prompt against multiple coding agents in parallel and compare results

AgentTester

⚠️ Experimental — This project is under active development. APIs, config format, and CLI flags may change without notice.

Send a single prompt to multiple coding agents running in parallel and compare the results. Each agent works in its own git worktree on a separate branch so they never interfere with each other.

Install

uv pip install -e ".[dev]"

Quick Start

# List built-in agents
agent-tester agents

# Run two agents on the same prompt
agent-tester run "Add unit tests for the auth module" --agents claude,aider

# Use a prompt file
agent-tester run --prompt-file task.md --agents claude,codex,aider

# Keep worktrees for manual inspection
agent-tester run "Refactor logging" --agents claude,aider --keep-worktrees

How It Works

1. You provide a prompt and select agents
2. AgentTester creates a git worktree + branch for each agent from the current HEAD
3. All agents run concurrently, each in its own worktree
4. Agent output streams to the terminal with colored prefixes
5. A markdown comparison report is generated with diff stats and timing
6. Worktrees are cleaned up (branches are preserved for git diff)

Branches are named agenttester/<run-id>/<agent-name> so you can compare results:

git diff agenttester/a3f2c1d0/claude agenttester/a3f2c1d0/aider

Configuration

Copy config.example.yaml to agent-tester.yaml (or agent-tester.yml) in your target repo to customize agents. Built-in presets are available for claude, aider, and codex.

Config file discovery

Auto-detected local config files must use a .yml or .yaml extension. The following names are checked in order:

agent-tester.yaml
agent-tester.yml
.agent-tester.yaml
.agent-tester.yml

You can also pass a config file explicitly — no extension required:

agent-tester run "Fix the bug" --agents claude --config /path/to/myconfig

A global config at ~/.config/agenttester/config.yml or ~/.config/agenttester/config.yaml is merged automatically. Local project config takes precedence over global, which takes precedence over built-in presets.

Reports

Reports are written to ~/.config/agenttester/projects/<repo-name>/ by default. You can override this per-project:

Local config (agent-tester.yaml in your repo):

reports_dir: ~/my-reports/myproject

Global config (~/.config/agenttester/config.yml), per named project:

projects:
  myproject:
    reports_dir: ~/my-reports/myproject

Local config takes priority over the global projects: setting.

Command Placeholders

• {prompt} — replaced with the shell-escaped prompt text
• {prompt_file} — replaced with a path to a temp file containing the prompt
• If neither placeholder is present, the prompt is piped to the agent via stdin

Agent Settings

Field	Description	Default
command	Shell command template	(required)
commit_style	auto (agent commits) or manual (agenttester commits)	auto
timeout	Max seconds before the agent is killed	600
env	Extra environment variables (key-value map)	{}

Skills

Skills are markdown instruction files prepended to every agent prompt. They tell agents what they are allowed to do and how to behave. AgentTester ships with four built-in skills:

Skill	Description
editing.md	Permission to read and edit files freely; look for reusable code before writing new code; prioritise readability
testing.md	Run the test suite and linter after making changes; don't mark a task complete until tests pass
git.md	Permitted git operations (branch, commit, push, pull, rebase); never push to the default branch
bash.md	Permitted bash operations scoped to code editing and testing; no system-level changes outside the worktree

Overriding or extending skills

You can override any built-in skill or add new ones at two levels:

Global (~/.config/agenttester/skills/): applies to all projects.

Local (.agent-tester/skills/ inside your repo): applies to this project only.

A skill file with the same name as a built-in replaces it entirely. New filenames add additional instructions. Skills are always output in priority order — built-ins first, global skills second, local skills last — so user-defined instructions appear closest to the prompt and carry the most weight with the model.

~/.config/agenttester/skills/testing.md   # overrides built-in testing skill globally
your-repo/.agent-tester/skills/testing.md # overrides for this project only
your-repo/.agent-tester/skills/style.md   # adds a new skill for this project

Interactive Model REPL

For comparing responses from vLLM model servers interactively, with persistent conversation history within a session:

agent-tester repl                        # auto-discovers agent-tester.yaml, falls back to global config
agent-tester repl --config custom.yaml   # explicit config path

The REPL discovers any agent in your config whose command matches the agenttester query pattern, fans out each prompt to all of them in parallel, and maintains separate conversation history per model. Use /reset to clear history or exit to quit.

Config resolution follows the same priority as run: global config first, then local (or explicit) config, with local taking precedence on conflicts. Models defined only in the global config are available in the REPL even when a local config is present.

See config.example.yaml for example vLLM agent entries.

Development

uv pip install -e ".[dev]"
ruff check src/ tests/
ruff format src/ tests/
pytest

Docker

# Run against the current directory
docker compose run --rm agent-tester run "Fix the bug" --agents claude

# Run against a different repo
REPO_PATH=/path/to/repo docker compose run --rm agent-tester run "Add tests" --agents claude,aider

Library Usage

import asyncio
from pathlib import Path
from rich.console import Console
from agenttester import Orchestrator, load_config
from agenttester.config import get_reports_dir

async def main():
    repo = Path(".").resolve()
    agents = load_config()
    selected = [agents["claude"], agents["aider"]]
    orch = Orchestrator(repo, Console(), get_reports_dir(repo))
    results = await orch.run("Add unit tests", selected)
    for r in results:
        print(f"{r.agent_name}: exit={r.exit_code} duration={r.duration:.1f}s")

asyncio.run(main())