# MCP Liveness

> Whether a stock client can actually use an MCP server from the registry. Free, no key.

A registry listing is a claim the publisher typed. Nothing verifies it at publish time,
so an agent picking a server out of the catalogue has no way to know whether the endpoint
answers, whether it wants a credential, or whether a credential can be obtained at all.
This makes one `initialize` call with no credential and says what a stock client gets.
On a 401 it walks the discovery chain the spec defines — RFC 9728, RFC 8414, RFC 7591 —
and reports whether a client nobody has heard of could register itself, or whether a
person has to create one. Both are HTTP 401 and the registry lists them identically.
Measured on a random sample of 1200 remote listings on 2026-09-12: 63.0% answer a stock client, 21.8% want a credential, and 14.8% are not an MCP server at the address they gave. Of the ones wanting a credential, 17.2% published nothing a stock client could discover.
Do not probe the catalogue yourself. Every remote listing is probed once a month and the
answers are served as static files, so reading them costs one request instead of 19,000
and costs the registry's servers nothing at all. `/v1/alive` is for a single name you
care about right now; the files are for choosing.
Every request identifies itself as `agentwares-mcp-liveness/0.1 (+https://agentwares-agentcheck.vercel.app/bot)`. It never sends a credential, never
registers a client, never retries a refusal and never evades anything.

## Links

- [Check one server](https://agentwares-mcp-liveness.vercel.app/v1/alive?name=io.github.agentwares/mcp-liveness): GET, JSON, no key — probes live
- [Every listing, precomputed](https://agentwares-mcp-liveness.vercel.app/index.ndjson): one line per remote listing with its last outcome; fetch this instead of probing
- [The ones to skip](https://agentwares-mcp-liveness.vercel.app/unreachable.ndjson): only the listings whose endpoint is not an MCP server — the smallest useful file
- [What is in those files](https://agentwares-mcp-liveness.vercel.app/index.meta.json): counts, causes, sizes, build time
- [The survey](https://agentwares-mcp-liveness.vercel.app/v1/survey): the sampled population numbers
- [MCP server](https://agentwares-mcp-liveness.vercel.app/mcp): Streamable HTTP, no auth
- [Server card](https://agentwares-mcp-liveness.vercel.app/server.json)

## MCP tools

- `mcp_liveness_check` (name, skipCredentialCheck?): Given a server's exact name in the official MCP registry, make one `initialize` call to
the endpoint its listing names and report what a client with no credential gets.

Outcomes: `usable` (it connected and negotiated a protocol version), `needs_credential`
(401 or 403 — the answer then says whether a credential can be obtained in-band or
whether a person has to create one), `charged` (402, access is for sale), `unreachable`
(the listed endpoint is not an MCP server: wrong URL, dead host, or a 200 that is not
JSON-RPC), `local_only` (no remote endpoint; it must be spawned as a process), and
`not_listed` (no server with that exact name).

Call this before spending a call on a server you found in the catalogue. Roughly two in
five remote listings do not answer a stock client.
- `mcp_liveness_explain_outcomes`: Return the six outcomes this server can report, what each means for an agent choosing a server from the registry, and what to do next for each. Makes no request and costs nothing; call it once to interpret mcp_liveness_check results.