Glossary · Network and discovery
AI Catalog
A JSON document that lists a host's AI artifacts, such as A2A Agent Cards and MCP Server Cards, often served at /.well-known/ai-catalog.json.
An AI Catalog is a JSON document that lists the AI artifacts a host offers. Each entry says what kind of artifact it is, with a media type such as application/a2a-agent-card+json for an A2A Agent Card or application/mcp-server-card+json for an MCP Server Card, and then either links to the artifact or carries it inline. The catalog doesn’t define what an Agent Card or a server card contains; each protocol keeps its own format.
Why it exists. The well-known URI for A2A, /.well-known/agent-card.json, holds one card per domain. A company with several agents, or a platform hosting agents for many businesses, can’t list them all there. A catalog can list any number of agents, MCP servers, skills and other artifacts in one file, and it can point to other catalogs.
Where to find one. A host may serve its catalog at /.well-known/ai-catalog.json, or anywhere else and point to it with an HTTP Link header or an HTML <link> element using the ai-catalog relation. The document’s media type is application/ai-catalog+json.
Minimum content. A specVersion string and an entries array. Each entry needs an identifier, a type, and exactly one of url or data. Adding a host object that names the catalog’s operator makes the catalog “Discoverable” (Level 2); signed Trust Manifests on entries make it “Trusted” (Level 3).
Status. The specification is an editor’s draft (October 1, 2026). An open A2A pull request proposes it as A2A’s preferred way to find agents, and the open MCP proposal for server cards uses the same file for HTTP discovery. Neither has been merged.
Trust. Like an Agent Card, a catalog is a claim by whoever controls the file. Its identifiers and URLs don’t prove who publishes an artifact; the optional signed Trust Manifest is the specification’s answer to that.
Questions
- Does an AI Catalog replace agent-card.json?
- Not today. A2A 1.0 clients look for /.well-known/agent-card.json, and A2A has not adopted the catalog yet. Publishing both costs little: the catalog lists the card, and the card stays where current clients expect it.
- Is an AI Catalog a standard?
- It is a draft from the Agent Card Working Group, and the draft says it may change at any time. A2A and MCP proposals point to it, but neither has merged it into its specification.