FACTANKER Pro · machine infrastructure
MCP Contract Watch
Reachability, tool-contract changes and breaking changes for more than 20,000 public MCP servers, probed continuously since August 2026 — browsable and queryable today; per-server alerts and feeds with Pro (in preparation).
What it is
Reachability, tool-contract changes and breaking changes for more than 20,000 public MCP servers, probed continuously since August 2026 — browsable and queryable today; per-server alerts and feeds with Pro (in preparation).
Sources: Our own measurement: MCP handshake and tools/list against every registry-listed public endpoint; three million probes on record.
Update cadence: Continuous probing; contract diffs within hours; history since August 2026 per server.
What we measure, right now
| Measure | Count |
|---|---|
| Public MCP servers observed | 21,082 |
| Currently answering | 20,226 |
| Went silent (reachable before, not now) | 856 |
| Came back after silence | 793 |
| Servers with at least one breaking contract change | 1,804 |
| Breaking changes recorded | 5,789 |
| Probes | 3,179,317 |
| Days observed | 50 |
A breaking change is a tool removed, renamed, or given a changed required-input schema between two probes — the thing a plain uptime monitor never sees, because the server still answers 200. Browse the observatory → · Read the analysis →
What Pro adds: per-server Atom feed and webhook that fires on silence, return and every contract diff; the full probe history as JSONL; an API that returns the current tool contract and its diff against any earlier date.
Who uses it
teams running agents against third-party MCP servers, MCP registry and gateway operators, security and platform engineering, server authors watching their own contract.
Agent reliability
Your agent calls a third-party MCP server; the server renames a tool overnight; your agent fails silently. Watch fires before your users notice.
Registry and gateway operators
Mark listings as silent, returned or changed from our probes instead of running your own.
Security and change control
A changed required-input schema is a changed attack surface; get the diff, not just an alert.
Server authors
Verify what the world sees of your contract after every deploy.
Why this exists as a paid product
MCPWatch sells schema-change alerts from $49/month for 50 servers; AlertsDown and OneUptime sell MCP uptime. We watch every public server, not a list you maintain. Every FACTANKER figure stays free to read and to query one at a time; Pro is for the people who need all of it, fast, with a feed and someone to e-mail.
Pricing
Introductory prices. Payment is not live yet — write to us and we set you up by hand; billing starts when the payment page does.
| Plan | What you get | Price |
|---|---|---|
| Free | Everything public: pages, REST API, MCP server, Markdown views, evidence links. Rate-limited, no key, no signup — this does not change. | $0 |
| Pro — one product | API key without the public rate limit, bulk CSV/JSONL export of the product's tables, change feed (Atom) or webhook (in preparation), e-mail support within one working day. | $49/month or $490/year |
| Pro — all five | The same for every Pro product, one key. | $149/month or $1490/year |
| Enterprise / data licence | Full feed or dump, SLA, redistribution rights under the EU database right (Enerlio GmbH), custom serialisation, invoice billing. | on request |
The underlying official data is public domain and stays free; what Pro sells is the normalised, resolved, evidence-linked compilation, its history and its delivery. Prices are net, excluding VAT; business customers only; invoices in USD or EUR; contract terms on request. Terms of use: /nutzung.
Questions
What counts as reachable?
A completed MCP handshake and a tools/list answer within our timeout. A 200 from an HTTP server that is not speaking MCP is not reachable.
Do you probe private servers?
No. Only endpoints that are publicly listed in registries and answer without credentials; authenticated endpoints are recorded as such.
How fast will an alert be?
Alerts and feeds are in preparation for Pro: within the probe interval after the change, with the two contract versions and the diff in the item. Today the change is visible on the server's page and via the API.
FACTANKER Pro is a commercial offer of Enerlio GmbH. Everything public on this site stays free and keyless.