@demystify/tools-mcp

A local MCP (Model Context Protocol) server that exposes the Demystify tool engines to any MCP client (Claude Desktop, IDE agents, …) over stdio.

The AI passes structured input; a golden-verified engine computes the output. No model is invoked inside the tool, so results are deterministic and never hallucinated — an LLM asking gst-calculator for ₹1,000 at 18% gets exactly ₹1,180.00 every time, computed by the same engine the website uses. And it runs with zero network access — the engines and their schemas are bundled.

Run

# from a published install
npx demystify-tools-mcp

# from this repo
pnpm --filter @demystify/tools-mcp build
node packages/mcp/dist/cli.js

Claude Desktop

claude_desktop_config.json:

{
  "mcpServers": {
    "demystify-tools": { "command": "demystify-tools-mcp" }
  }
}

What it exposes

Every tool that has a pure engine binding (@demystify/tools-engines/api) — the same zod I/O the web app, REST API and self-hosted runner use. Today that is the verified pure-lane set (JSON/base64/hash/UUID/JWT, epoch & cron, GST/GSTIN/ UPI/gold/amount-to-words, JSON→CSV/TS/Schema). The list grows one batch at a time as more engines are bound; the server always mirrors the bindings.

Each tool's inputSchema is derived from its zod schema (a client hint); every call is still validated against the real zod schema server-side, and invalid input comes back as an MCP tool error the model can read and correct.

Protocol

Implements the tools surface of MCP (initialize, tools/list, tools/call, ping) as newline-delimited JSON-RPC 2.0 over stdio — no third-party runtime dependencies, so the trust story (deterministic, offline, no tracking) holds end to end. The pure handler (src/server.ts) is unit-tested independently of stdio.

Status

Pre-1.0, versioned but not yet published — see the repo's docs/verification/user-actions.md (U19) for the publish checklist.