addrbookFor publishers

How addrbook checks

addrbook checks whether the AI agents that public registries list actually answer. This page says exactly what the check does.

Identifies itself as
addrbook-probe/1 (+https://addrbook.com/probe)
Opt-outs
optout@addrbook.com, honoured within 24 hours

What each check sends

A check reads; it never pays, signs up or changes anything. By protocol:

MCP servers
  1. An initialize request.
  2. The notifications/initialized notice.
  3. A tools/list request, to count the tools and notice when they change.

No tool is ever called.

x402 endpoints
An unpaid GET, or an empty POST with no body when the route only accepts POST. The endpoint should answer 402 with its payment requirements. addrbook never pays and never sends a request body.
A2A agents
A GET of the agent card at /.well-known/agent-card.json, or agent.json for older agents.
Websites
A GET of the page; any status below 400 counts as answering.

How often, and how politely

  • Every hour while an endpoint answers.
  • After 4 to 10 failures in a row, once a day; after more than 10, once a week.
  • One request at a time per host, at least one second apart.
  • Before fetching web pages and agent cards, the probe reads the host's robots.txt (once a day) and honours it.
  • Only public addresses on ports 80 and 443, at most three redirects, eight seconds per check, and capped response sizes.

What it records

The outcome, the HTTP status, the response time, and for MCP servers the number of tools and a fingerprint of the list. Individual results are kept for 30 days, hourly summaries after that. Response bodies are not stored.

What the statuses mean

A status describes what addrbook observed and when, not whether an agent is any good.

Live
Its best endpoint answered the latest check.
Live, sign-in required
It answered with a request for credentials. That counts as answering.
Degraded
The latest check failed, but it answered within the last 24 hours.
Unreachable
It has not answered in the last 24 hours, or has not answered any check yet. The page says since when.
Not checked yet
addrbook has not checked it yet. The page says since when it is listed.
Nothing to check
Its listings name nothing addrbook can reach, such as a local-only MCP server.
Opted out
Its publisher asked addrbook to stop checking it.

Opting out, corrections and removal

Write to optout@addrbook.com from an address at the domain concerned, or with another proof that you run the agent. Opt-outs from checks are honoured within 24 hours. The same address handles corrections and requests to remove a profile. Owners will be able to claim their profiles directly once claims open.