Irrational MCP Server

Irrational

A field guide to the mistakes your mind makes — and an open, adversarial behavioural-bias engine you can call from your own AI or any MCP agent.

→ irrational.pages.dev · Field guide · Connect via MCP · Sources

Irrational runs no AI model. It provides the curated adversarial framework, a 22-bias catalogue, and a stateless scaffold — delivered as a public field guide and an open MCP tool — and the reasoning is done by whatever model you or your agent already have. No API keys. No stored decisions. Nothing leaves you.

A frontier model already knows the biases, so the value isn't informational — it's behavioural: a plain LLM is trained to agree, while Irrational has a fixed adversarial contract (assume you're biased, refuse to validate, argue the other side) that an agent can invoke systematically — even on its own draft reasoning.

What an audit looks like

You: "We should rewrite our 6-year-old backend from scratch this year — we've already spent two months on a POC that went well, and I'm confident we can finish in six."

THE CALL — Don't greenlight the big-bang rewrite. Carve off the worst module first, with a hard 3-month checkpoint. Confidence the 6-month plan succeeds: ~25% — mostly sunk cost + the planning fallacy.

THE AUDIT — Those "two months on a POC" are gone either way, but they're doing most of the talking (sunk cost). "About six months" is a best-case with no reference class — rewrites of mature systems routinely run 2–3× (planning fallacy)…

Verdict-first, every bias tied to your own words, grounded in a cited catalogue. See the full worked examples →

Add it to your AI

Listed on the official MCP Registry as io.github.urbanmorph/irrational. Connect any MCP client to the live endpoint — no install, no keys:

# Claude Code
claude mcp add --transport http irrational https://irrational.pages.dev/mcp/server

…or point any MCP client at https://irrational.pages.dev/mcp/server:

{
  "mcpServers": {
    "irrational": {
      "type": "http",
      "url": "https://irrational.pages.dev/mcp/server"
    }
  }
}

Tools: analyze_decision (the adversarial audit) · list_biases · get_bias. Pass language for a reply in another language, or structured: true for parseable JSON.

What's inside

• Field guide — 22 cognitive biases grouped by Buster Benson's four problems the brain solves, each with the question that breaks its spell and a verified citation.
• The engine — an MCP server exposing analyze_decision, list_biases, get_bias. analyze_decision returns a verdict-first directive your model executes. The discipline is ours; the reasoning is yours.
• The web forge — type a decision; it assembles the adversarial prompt in your browser and hands off to your AI. No model runs here.
• Pen-and-paper audit — the whole method on one printable page.

Stack

Astro (pure static) · Cloudflare Pages · a hand-rolled, dependency-free JSON-RPC MCP endpoint as a Pages Function. No runtime model, no database. Single source of truth: src/data/biases.ts feeds both the web and the MCP.

Develop

npm install --ignore-scripts   # we don't use image optimization, so skip sharp's native build
npm run dev                    # http://localhost:4321
npm test                       # vitest — engine + catalogue (29 tests)
npm run build                  # static pages

The MCP endpoint is a Cloudflare Pages Function — run it locally with npx wrangler pages dev dist.

Contributing

Translations, proposed biases, and worked examples are welcome — see CONTRIBUTING.md. This project also publishes a public PDGI scorecard.

Licence

Code is MIT. The bias-catalogue text (definitions, examples, and the curated prose in src/data/) is additionally available under CC-BY-4.0. Every claim is cited — see /sources.

Built by Urban Morph.