Open Model Gym

Run agent tests across a matrix of models × runners × scenarios.

It isn't hard for any agent to do ok with opus, but lets scale things in the other direction. What do we have to break things down to.

Quick Start

just install   # one-time setup
just run       # run full matrix (3 reps each)
just report    # view results

How It Works

The test harness runs every combination of models, runners, and scenarios defined in your matrix. Each test runs multiple times (default 3) and keeps the worst result — if a test fails even once, it's marked failed. This catches flaky passes.

Configuration

Edit config.yaml to define your test matrix:

Models

LLMs to test against. Supports any provider (Anthropic, OpenAI, Ollama, etc.):

models:
  - name: opus
    provider: anthropic
    model: claude-opus-4-5-20251101

  - name: qwen3-coder
    provider: ollama
    model: qwen3-coder:64k

  - name: gpt4
    provider: openai
    model: gpt-4-turbo

Runners

Agent frameworks that execute the tests. Each runner has its own binary, type, and configuration:

runners:
  # Goose agent with extensions
  - name: goose-full
    type: goose
    bin: goose                    # path to binary (can be absolute)
    extensions: [developer, todo, skills]
    stdio:
      - node mcp-harness/dist/index.js

  # OpenCode agent
  - name: opencode
    type: opencode
    bin: opencode                 # path to binary
    stdio:
      - node mcp-harness/dist/index.js

  # Custom goose binary path
  - name: goose-dev
    type: goose
    bin: /path/to/my/goose-dev
    extensions: [developer]

Supported runner types:

• goose — Goose agent framework
• opencode — OpenCode agent framework
• pi — Pi coding agent

Runner Details

Each runner has different setup requirements, MCP integration methods, and session handling.

Goose

Goose is Block's open-source coding agent with built-in MCP support.

Setup: Install via brew install goose or from source.

MCP Integration: Native support. The harness writes a config.yaml to an isolated .goose-root/ directory with extensions and MCP servers:

extensions:
  developer:
    enabled: true
  mcp_harness:
    type: stdio
    enabled: true
    cmd: node
    args: [mcp-harness/dist/index.js]

Session Handling: Uses --name <session> for named sessions, --resume to continue:

• Turn 1: goose run -i <prompt> --name <session>
• Turn 2+: goose run -i <prompt> --name <session> --resume
• Single-turn: goose run -i <prompt> --no-session

OpenCode

OpenCode is a terminal-based coding agent.

Setup: Install via their website or package manager.

MCP Integration: Native support. The harness writes an opencode.json config to the workdir:

{
  "mcp": {
    "harness": {
      "type": "local",
      "command": ["node", "mcp-harness/dist/index.js"],
      "enabled": true
    }
  },
  "model": "anthropic/claude-opus-4-5-20251101"
}

Session Handling: Uses --continue to resume the last session in the working directory:

• Turn 1: opencode run "<prompt>"
• Turn 2+: opencode run --continue "<prompt>"

⚠️ OpenCode doesn't support named sessions, so multi-turn scenarios exclude it.

Pi

Pi is a lightweight coding agent that requires an adapter for MCP support.

Setup:

# Install Pi
npm install -g @anthropic/pi   # or from source

# Install the MCP adapter (required for MCP tools)
pi install npm:pi-mcp-adapter

The just install recipe auto-installs pi-mcp-adapter if missing.

MCP Integration: Via pi-mcp-adapter. The harness dynamically writes a .pi-mcp.json config to the workdir:

{
  "mcpServers": {
    "harness": {
      "command": "node",
      "args": ["mcp-harness/dist/index.js"],
      "lifecycle": "eager",
      "env": { "MCP_HARNESS_LOG": "<workdir>/tool-calls.log" }
    }
  },
  "settings": { "directTools": true }
}

Key settings:

• directTools: true — Registers MCP tools directly in Pi's tool list (no wrapper)
• lifecycle: "eager" — Connects to MCP servers at startup

Model Configuration: Pi requires custom models (like Ollama) to be defined in models.json. The harness automatically generates this config in an isolated .pi-root/ directory and sets PI_CODING_AGENT_DIR to use it:

{
  "providers": {
    "ollama": {
      "baseUrl": "http://localhost:11434/v1",
      "api": "openai-completions",
      "apiKey": "ollama",
      "models": [{ "id": "model-name", "name": "Model Name", ... }]
    }
  }
}

The harness copies auth.json from your real Pi config (~/.pi/agent/) so API keys work.

Session Handling: Uses --session <path> for file-based sessions, --continue to resume:

• Turn 1: pi -p --session <path> "<prompt>"
• Turn 2+: pi -p --continue --session <path> "<prompt>"
• Single-turn: pi -p --no-session "<prompt>"

The -p flag runs Pi in non-interactive "print" mode for automation

Matrix

Define which scenarios run against which models/runners:

matrix:
  - scenario: file-editing
    models: [opus, qwen3-coder]      # omit to run all models
    runners: [goose-full, opencode]  # omit to run all runners

  - scenario: everyday-app-automation
    # runs against ALL models and ALL runners

Scenarios

Scenarios live in suite/scenarios/ as YAML files:

name: file-editing
description: Create and edit files
prompt: |
  1. Create joke.md containing a short joke
  2. Edit hello.rs to add a debug function

setup:
  hello.rs: |
    fn main() { println!("Hello!"); }

validate:
  - type: file_exists
    path: joke.md
  - type: file_matches
    path: hello.rs
    regex: "fn\\s+debug"

Validation Rules

Rule	Description
file_exists	File exists at path
file_not_empty	File exists and has content
file_contains	File contains literal string
file_matches	File matches regex pattern
command_succeeds	Shell command exits 0
tool_called	MCP tool was called with matching args (regex supported)

Tool call validation example:

validate:
  - type: tool_called
    tool: slack_search_messages
    args:
      query: /quarterly.?review/    # regex pattern
  - type: tool_called
    tool: jira_create_issue
    args:
      summary: /Q1.*Review/
      description: /David Brown/

MCP Harness

Mock MCP server providing simulated tools for testing agent tool-use without hitting real APIs.

cd mcp-harness && npm install && npm run build

Available tools: gdrive, sheets, salesforce, slack, calendar, gmail, jira, github

Each tool returns realistic mock data. Tool calls are logged to tool-calls.log in the workdir for validation.

Commands

Command	Description
just run	Full test run (3 reps each, worst kept)
just test	Quick run (1 rep each)
just scenario <name>	Run specific scenario
just agent <name>	Run specific agent
just report	Open HTML results

CLI Flags

# Filter by scenario, model, or runner
npx tsx src/runner.ts --scenario=file-editing --model=opus --runner=goose

# Control repetition count
npx tsx src/runner.ts --run-count=5

# Don't auto-open browser
npx tsx src/runner.ts --no-open

Output

• report.html — Live-updating HTML matrix showing pass/fail status, duration, and validation details
• logs/ — Full agent output logs for each run