The full upstream README, mirrored here for reference. Install config, tool schemas, adoption signals, and an original overview live on the Check Digits listing page.
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.
Discontinued September 2026. The hosted endpoints are gone and the npm packages are deprecated. The code still runs locally over stdio if you want it; the export-control tables are frozen at their 2026-08-27 edition.
| 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 |
Remote, over streamable HTTP. No install, no account:
Local, over stdio:
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.
The row also carries a session id, and it is derived from the network the request came from, truncated to a /24 or /48 before hashing, never the full address. Hashing the whole IP would not have anonymised it: the IPv4 space is 32 bits and the other inputs are public, so the id was walkable back to one address until this was fixed on 2026-08-10. Each server's README states the complete recorded row rather than only what is left out.
Every tool declares readOnlyHint, a complete inputSchema and an
outputSchema, so a client can tell what a call will do before making it and
what shape comes back. The transport refuses to start a server whose tools do
not state their annotations, rather than defaulting them to something reassuring.
See CLAUDE.md for the operating manual.
MIT