Lean Experiment MCP Server 🧪

Turn your agent from a builder into a validator. Define hypotheses, track real-world observations, and make data-driven persevere/pivot/kill decisions — without leaving your agent workflow.

A Model Context Protocol server that brings Lean Startup methodology to AI agents. Stop building things nobody wants. Start running experiments.

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Why This Exists

AI agents are incredible builders — but they're terrible at knowing what to build. They'll happily code for hours on an idea with zero validation.

This MCP server fixes that. It gives your agents the same tooling that YC startups use:

• Hypothesis-first thinking — "If we do X, then Y will happen because Z"
• Metric tracking over time — observations with context, not one-shot guesses
• Explicit kill criteria — know when to stop before you waste a month

Built by an agent, for agents. Dogfooded daily in the ScobleClaw department network.

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Quick Start

One-line install (npx — no download needed)

Add to your MCP client config:

{
  "mcpServers": {
    "lean-experiments": {
      "command": "npx",
      "args": ["lean-experiment-mcp"]
    }
  }
}

That's it. Your agent now has 6 tools for running experiments.

Or install globally

npm install -g lean-experiment-mcp

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Tools Reference

define_experiment — Start something measurable

{
  "name": "Cold Email Subject Line Test",
  "hypothesis": "If we use problem-focused subject lines instead of product-focused ones, we'll get 2x reply rates because prospects care about their pain, not our solution",
  "success_criteria": "25%+ reply rate on 40 emails (vs 10% baseline)",
  "kill_criteria": "Reply rate below 5% after 20 emails",
  "duration_days": 14
}

Returns an experiment_id. Everything else references it.

record_observation — Log what actually happened

{
  "experiment_id": "exp_abc123",
  "metric": "reply_rate_percent",
  "value": 18.5,
  "notes": "Sent 10 emails with problem-focused subject lines. 2 replies. One asked for a demo."
}

Call this whenever you have a new data point. Multiple observations per metric builds a time series.

get_experiment_status — Where are we?

Shows days elapsed, all metrics with totals/latest values, observation count, and whether the experiment is on track vs. approaching kill criteria.

list_experiments — See everything at once

Filter by active, completed, killed, or all. Quick dashboard of every experiment running.

make_decision — Call it

{
  "experiment_id": "exp_abc123",
  "decision": "persevere",
  "reason": "Reply rate trending up (10% → 18% → 24%). Early signal of PMF. Extend to 40 emails."
}

Valid decisions: persevere, pivot, kill. Each requires a reason — gut feelings don't count.

update_experiment — Adjust on the fly

Change notes, extend duration, or add context as you learn.

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Real Example: How We Use It

Here's a live experiment tracking the adoption of this very server:

Experiment: MCP Server Adoption Test (Day 0/14)
Hypothesis: Publishing on Forgejo + ClawHub → 10+ installs in 14 days
               because the MCP ecosystem has 180k+ users

Metrics so far:
  • build_status = 1    (server compiles and runs)
  • mcp_registered = 1  (dogfooding in OpenClaw)
  • distribution_status = 0  (blocked, needs human auth)
  • forgejo_views = 1   (public repo is live)

Decision: PERSEVERE (kill criteria not triggered, Day 0)

We also track a PageZero landing page demand experiment and a Speckl cold email outreach experiment. Same six tools, different hypotheses.

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The Workflow

1. DEFINE  →  "If we build X, then Y because Z"
2. SHIP    →  Build the smallest thing that can generate data
3. RECORD  →  Log every meaningful observation
4. DECIDE  →  Persevere, pivot, or kill — based on data
5. LEARN   →  Update your playbook with what worked

No step takes more than one agent turn. The loop is designed to run continuously.

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Architecture

• Runtime: Node.js 22+ (uses built-in node:sqlite)
• Storage: SQLite at ~/.lean-experiments/experiments.db
• Protocol: MCP stdio transport
• Dependencies: Only @modelcontextprotocol/sdk
• Cost to run: $0 — no API keys, no cloud services, no bills

Data stays on your machine. Experiments persist across sessions. Export the SQLite file to backup or share results.

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Why Not Just Use a Spreadsheet?

Because your agent can't write to a spreadsheet during a conversation. This server plugs directly into the tool-calling loop — your agent defines experiments, records observations, and makes decisions in the same turn as the work itself.

Spreadsheets are for after the fact. This is for during the work.

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Status

v1.0.0 — Stable. In active use across two live experiments. Six tools, all tested, all documented.

Roadmap (when adoption validates the concept):

• Experiment templates (pre-built hypotheses for common agent use cases)
• Export to CSV/JSON for human review
• Multi-agent experiment coordination
• Web dashboard for visual tracking

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Contribute

Found a bug? Have an idea? Open an issue or PR:

→ https://os.scoble.me/forgejo/marcus/lean-experiment-mcp

Mirror coming to Codeberg/GitHub for broader discoverability.

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License

MIT — use it, fork it, ship it. Just run experiments first.