Registry Rot Watch: liveness + successor-contract verdicts for MCP endpoints. Agents select MCP tools from a registry that tests nothing and deletes essentially nothing: of 28,933 remote endpoints listed 2026-10-16, 13% did not work, and of 448 server migrations only 4 could be checked for contract continuity because nobody held a pre-move snapshot — so an agent cannot tell mid-task whether an endpoint is live, auth-gated, dead, or quietly succeeded by a different contract. Registry Rot Watch holds the pre-move snapshot vault (tool-name set + per-tool contract hashes, taken while an endpoint is live at its listed address) and answers, mid-task and agent-callable: a liveness verdict (LIVE / AUTH_GATED / NO_RESPONSE / DEAD) from the vault or a live anonymous MCP probe, a successor verdict (MOVED-LIVE-SAME-CONTRACT / MOVED-CONTRACT-CHANGED naming the added, removed and schema-changed tools / MOVED-DEAD) from the stored snapshot, and watch alerts when a depended-on endpoint changes status or contract. A probe that succeeds without a readable tool list retains the last-known contract and issues no change verdict — contract-unknown is not a delta.
Verdict query $0.01/call (x402) · Dependency watch $2.99/endpoint/mo · Publisher verified-successor listing $9.99/mo. One free verdict query per operator, ever. There is no perpetual free tier.
Documented limits: the NO_RESPONSE population publishes neither RFC 9728 nor RFC 8414 metadata and stays honestly NO_RESPONSE — a property of the population, not the classifier. A bare 403 without a Bearer challenge or metadata is not guessed AUTH_GATED. Successor verdicts need a baseline: a stored pre-move snapshot, or one you supply. Watches check on a 6-hourly cadence. Probing is anonymous and wire-side only (MCP initialize + tools/list); private, loopback, link-local and reserved targets are refused.
How it works: POST /register for a token, GET /verdict?url= for a vault verdict (one free per operator, then $0.01/call via x402), POST /probe {url} for a live probe at the same price, POST /successor {old_url, new_url} for a successor verdict, POST /subscribe {tier:"watch", endpoint} ($2.99/endpoint/mo) then POST /watch to watch an endpoint, POST /subscribe {tier:"publisher"} ($9.99/mo) then POST /listings for a verified-successor listing. MCP at /mcp with the same billing.
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