/harness:setup

Set up the Harness Evolver v3 in a project. Explores the codebase, configures LangSmith, runs baseline evaluation.

Prerequisites

Check for LangSmith API key — it can be in the environment, the credentials file, or .env:

python3 -c "
import os, platform
key = os.environ.get('LANGSMITH_API_KEY', '')
if not key:
    creds = os.path.expanduser('~/Library/Application Support/langsmith-cli/credentials') if platform.system() == 'Darwin' else os.path.expanduser('~/.config/langsmith-cli/credentials')
    if os.path.exists(creds):
        for line in open(creds):
            if line.strip().startswith('LANGSMITH_API_KEY='):
                key = line.strip().split('=',1)[1].strip()
    if not key and os.path.exists('.env'):
        for line in open('.env'):
            if line.strip().startswith('LANGSMITH_API_KEY=') and not line.strip().startswith('#'):
                key = line.strip().split('=',1)[1].strip().strip('\"').strip(\"'\")
print('OK' if key else 'MISSING')
"

If

MISSING

: "Set your LangSmith API key:

export LANGSMITH_API_KEY=lsv2_pt_...

or run

npx harness-evolver@latest

to configure."

The tools auto-load the key from the credentials file, but the env var takes precedence.

Resolve Tool Path and Python

# Prefer env vars set by plugin hook; fallback to legacy npx paths
TOOLS="${EVOLVER_TOOLS:-$([ -d ".evolver/tools" ] && echo ".evolver/tools" || echo "$HOME/.evolver/tools")}"
EVOLVER_PY="${EVOLVER_PY:-$([ -f "$HOME/.evolver/venv/bin/python" ] && echo "$HOME/.evolver/venv/bin/python" || echo "python3")}"

Use

$EVOLVER_PY

instead of

python3

for ALL tool invocations. This ensures the venv with langsmith is used.

IMPORTANT: Never pass

LANGSMITH_API_KEY

inline in Bash commands. The key is loaded automatically by the SessionStart hook (from credentials file or environment) and by each Python tool's

ensure_langsmith_api_key()

. Passing it inline exposes it in the output. If the key is missing, tell the user to run

export LANGSMITH_API_KEY=lsv2_pt_...

instead.

Phase 1: Explore Project (automatic)

find . -maxdepth 3 -type f -name "*.py" -not -path "*/.venv/*" -not -path "*/node_modules/*" -not -path "*/__pycache__/*" | head -30

Monorepo detection: if the project root has multiple subdirectories with their own

main.py

or

pyproject.toml

, it's a monorepo. Use AskUserQuestion to ask WHICH app to optimize before proceeding — do NOT scan everything.

Look for:

• Entry points: files with

  if __name__

  , or named

  main.py

  ,

  app.py

  ,

  agent.py

  ,

  graph.py

  ,

  pipeline.py

• Existing LangSmith config:

  LANGCHAIN_PROJECT

  /

  LANGSMITH_PROJECT

  in env or

  .env

• Existing test data: JSON files with inputs, CSV files, etc.
• Dependencies:

  requirements.txt

  ,

  pyproject.toml

To identify the framework, read the entry point file and its immediate imports. The proposer agents will use Context7 MCP for detailed documentation lookup — you don't need to detect every library, just identify the main framework (LangGraph, CrewAI, OpenAI Agents SDK, etc.) from the imports you see.

Detect virtual environments — check for venvs in the project or parent directories:

# Check common venv locations
for venv_dir in .venv venv ../.venv ../venv; do
    if [ -f "$venv_dir/bin/python" ]; then
        echo "VENV_FOUND: $venv_dir/bin/python"
        break
    fi
done

If a venv is found, use it for the entry point instead of bare

python

. The agent's dependencies are likely installed there, not in the system Python. For example:

../.venv/bin/python agent.py {input}

instead of

python agent.py {input}

.

Identify the run command — how to execute the agent. Use

{input}

as a placeholder for the JSON file path:

• .venv/bin/python main.py {input}

  — if venv detected (preferred)

• python main.py {input}

  — agent reads JSON file from positional arg

• python main.py --input {input}

  — agent reads JSON file from

  --input

  flag

• python main.py --query {input_json}

  — agent receives inline JSON string

The runner writes

{"input": "user question..."}

to a temp

.json

file and replaces

{input}

with the file path. If the entry point already contains

--input

(without placeholder), the runner appends the file path as the next argument.

If no placeholder and no

--input

flag detected, the runner appends

--input <path> --output <path>

.

Phase 2: Confirm Configuration (interactive)

Present all detected configuration in one view with smart defaults and ask for confirmation.

Use AskUserQuestion:

{
  "questions": [{
    "question": "Here's the configuration for your project:\n\n**Entry point**: {command}\n**Framework**: {framework}\n**Python**: {venv_path or 'system python3'}\n**Optimization goals**: accuracy (correctness evaluator)\n**Test data**: generate 30 examples with AI\n\nDoes this look good?",
    "header": "Setup Configuration",
    "multiSelect": false,
    "options": [
      {"label": "Looks good, proceed", "description": "Use these settings and start setup"},
      {"label": "Customize goals", "description": "Choose different optimization goals"},
      {"label": "I have test data", "description": "Use existing JSON file or LangSmith project"},
      {"label": "Let me adjust everything", "description": "Change entry point, framework, goals, and data source"}
    ]
  }]
}

If "Looks good, proceed": Use defaults — goals=accuracy, data=generate 30 with testgen. Skip straight to Phase 3.

If "Customize goals": Ask the goals question, then proceed to Phase 3 with testgen as default data source.

Use AskUserQuestion:

{
  "questions": [{
    "question": "What do you want to optimize?",
    "header": "Goals",
    "multiSelect": true,
    "options": [
      {"label": "Accuracy", "description": "Correctness of outputs — LLM-as-judge evaluator"},
      {"label": "Latency", "description": "Response time — track and minimize"},
      {"label": "Token efficiency", "description": "Fewer tokens for same quality"},
      {"label": "Error handling", "description": "Reduce failures, timeouts, crashes"}
    ]
  }]
}

Map selections to evaluator configuration for setup.py.

Phase 2.5: Mode Selection

{
  "questions": [{
    "question": "Evolution mode?",
    "header": "Mode",
    "multiSelect": false,
    "options": [
      {"label": "light", "description": "20 examples, 2 proposers, ~2 min/iter. Good for testing."},
      {"label": "balanced (Recommended)", "description": "30 examples, 3 proposers, ~8 min/iter. Best trade-off."},
      {"label": "heavy", "description": "50 examples, 5 proposers, ~25 min/iter. Maximum quality."}
    ]
  }]
}

Pass selection to setup.py as

--mode light|balanced|heavy

.

The mode determines testgen count:

• light

  : generate 20 examples

• balanced

  : generate 30 examples (default, current behavior)

• heavy

  : generate 50 examples

If "I have test data": Ask the data source question, then proceed to Phase 3 with accuracy as default goal.

Use AskUserQuestion with preview:

{
  "questions": [{
    "question": "Where should test inputs come from?",
    "header": "Test data",
    "multiSelect": false,
    "options": [
      {
        "label": "Import from LangSmith",
        "description": "Use real production traces as test inputs",
        "preview": "## Import from LangSmith\n\nFetches up to 100 recent traces from your production project.\nPrioritizes traces with negative feedback.\nCreates a LangSmith Dataset with real user inputs.\n\nRequires: an existing LangSmith project with traces."
      },
      {
        "label": "I have a file",
        "description": "Point to an existing file with test inputs",
        "preview": "## Provide Test Data\n\nSupported formats:\n- JSON array of inputs\n- JSON with {\"inputs\": {...}} objects\n- CSV with input columns\n\nExample:\n```json\n[\n  {\"input\": \"What is Python?\"},\n  {\"input\": \"Explain quantum computing\"}\n]\n```"
      }
    ]
  }]
}

If "Import from LangSmith": discover projects and ask which one (same as v2 Phase 1.9). If "I have a file": ask for file path.

If "Let me adjust everything": Ask all three original questions in sequence — confirm detection (entry point, framework, run command), then goals, then data source — using the question formats above.

Phase 3: Run Setup

Build the setup.py command based on all gathered information:

$EVOLVER_PY $TOOLS/setup.py \
    --project-name "{project_name}" \
    --entry-point "{run_command}" \
    --framework "{framework}" \
    --goals "{goals_csv}" \
    ${DATASET_FROM_FILE:+--dataset-from-file "$DATASET_FROM_FILE"} \
    ${DATASET_FROM_LANGSMITH:+--dataset-from-langsmith "$DATASET_FROM_LANGSMITH"} \
    ${PRODUCTION_PROJECT:+--production-project "$PRODUCTION_PROJECT"}

If "Generate from code" was selected AND no test data file exists, first spawn the testgen agent to generate inputs, then pass the generated file to setup.py.

Phase 4: Generate Test Data (if needed)

If testgen is needed, spawn it:

Agent(
  subagent_type: "harness-testgen",
  description: "TestGen: generate test inputs",
  prompt: |
    <objective>
    Generate 30 diverse test inputs for this project.
    Write them as a JSON array to test_inputs.json.
    </objective>

    <files_to_read>
    {all .py files discovered in Phase 1}
    </files_to_read>

    <output>
    Create test_inputs.json with format:
    [{"input": "..."}, {"input": "..."}, ...]
    </output>
)

Then pass

--dataset-from-file test_inputs.json

to setup.py.

Phase 5: Report

Setup complete!
  Project: evolver-{name}
  Dataset: {name}-eval-v1 ({N} examples)
  Evaluators: {list}
  Baseline score: {score}
  Config: .evolver.json

Next: run /harness:evolve to start optimizing.

Gotchas

• If

  .evolver.json

  already exists, ask before overwriting.
• If the agent needs a venv, the run command should activate it:

  cd {dir} && .venv/bin/python main.py

• No project venv detected: Before building the entry_point, check if

  .venv/bin/python

  or

  venv/bin/python

  exists in the project directory. If NOT, warn the user:

  WARNING: No Python venv found in this project (.venv/ or venv/).
  The entry_point should use the project's own Python, not ~/.evolver/venv/bin/python.
  Create one first: python3 -m venv .venv && .venv/bin/pip install -r requirements.txt
  

  Do NOT use

  ~/.evolver/venv/bin/python

  as the entry_point — that's for evolver tools only. Using it pollutes the evolver venv with agent dependencies.
• If LangSmith connection fails, check API key and network. The

  ensure_langsmith_api_key()

  function validates key format and rejects dummy/test keys with a warning.
• Eval concurrency defaults to 3 (runs 3 examples in parallel). If the agent can't handle parallel execution (writes to shared files, uses a fixed port, holds a DB lock), set

  eval_concurrency: 1

  in

  .evolver.json

  after setup.
• Companion plugin: For full proposer observability, recommend installing

  langsmith-tracing

  from

  langchain-ai/langsmith-claude-code-plugins

  . Each proposer's file reads, edits, and commits become visible in LangSmith.