toolstop

Small, stateless MCP servers. Each one does a single narrow job exactly, so an assistant can call it instead of guessing.

Every server runs on Cloudflare Workers at <name>.toolstop.dev, holds no state, and can also run locally over stdio.

Servers

Server	Does	Endpoint
check-digits	Validates check digits for IBAN, LEI, ISBN, GTIN/UPC/EAN, VIN, NPI, ISIN, ABA routing numbers and payment cards	https://check-digits.toolstop.dev

Connecting

Remote, over streamable HTTP. No install, no account:

{
  "mcpServers": {
    "check-digits": {
      "type": "url",
      "url": "https://check-digits.toolstop.dev"
    }
  }
}

Local, over stdio:

npx mcp-check-digits

Design

Stateless. No database, no vector index, no metered upstream API. A request is answered from its arguments alone. Servers scale to zero and an idle one costs nothing.

Zero runtime dependencies. No MCP SDK, no schema library. MCP over streamable HTTP is request/response, which makes hand-rolled dispatch small enough to be worth it: faster cold starts, and no supply chain.

Telemetry records shape and outcome, never argument values. A check-digit server that logged its input would be storing real IBANs and card numbers. The transport emits one row per request describing what kind of call happened and whether it succeeded. packages/_shared/transport.test.mjs asserts that no raw argument value can reach it.

Every tool carries readOnlyHint and a complete inputSchema, so a client can tell what a call will do before making it.

Repo layout

packages/_shared/     shared transport, dispatch and telemetry
packages/mcp-<name>/  one server
scripts/discover.mjs  derives the CI matrix from the filesystem
scripts/smoke.mjs     protocol check against a live endpoint

See CLAUDE.md for the operating manual.

Development

npm install
npm test                                # every server plus the shared transport
node scripts/smoke.mjs mcp-check-digits # protocol check against the live endpoint

License

MIT