This appendix describes how the MCP Registry server.json format
-(see modelcontextprotocol/registry)
-relates to AI Catalog, enabling MCP servers to be discovered alongside
-other AI artifacts through a unified catalog.
-+Note: The MCP ecosystem defines two distinct metadata documents -for servers. The Registry
-server.jsonis an installable package -descriptor (package coordinates, transports, environment variables). -The MCP Server Card (SEP-1649) -is a runtime discovery document at/.well-known/mcp/server-card.json-describing capabilities, tools, and authentication. An AI Catalog -entry can reference either artifact depending on the use case — use -server.jsonfor installable packages and Server Cards for -connectable HTTP endpoints.
This appendix describes how remote (HTTP-connectable) MCP servers +map to AI Catalog, enabling them to be discovered alongside other AI +artifacts through a unified catalog. The documented, supported path is +to reference each server's MCP Server Card +(SEP-2127) +as the artifact content of a Catalog Entry.
+A Server Card is a static discovery document for a single HTTP-based MCP
+server (its identity and connection details). It is distinct from the MCP
+Registry's server.json, an installable-package descriptor — a separate
+artifact type that this appendix does not address.
The MCP Registry defines a server.json format for describing MCP
-servers. Each server.json document captures everything needed to
-install, configure, and connect to a single MCP server: package
-coordinates (npm, PyPI, NuGet, OCI), remote endpoints (streamable-http,
-SSE), transport configuration, environment variables, and CLI arguments.
In AI Catalog terms, a server.json document is the artifact
-content — the native metadata that a Catalog Entry references. The
-AI Catalog does not duplicate or redefine server.json fields.
-Instead, it provides the discovery and trust layer that server.json
-does not address.
MCP server.json |
-AI Catalog Equivalent | -
|---|---|
server.json document (whole file) |
-Artifact content via entry url or data |
-
name (reverse-DNS identifier) |
-Entry identifier (mapped to URI form) |
-
title |
-Stays in the artifact (server.json carries its own title); entry displayName is omitted unless the artifact lacks a name |
-
description |
-Entry description |
-
version |
-Entry version |
-
repository |
-Entry metadata.repository |
-
packages[] (npm, pypi, nuget, oci) |
-Inside the artifact — not surfaced in catalog | -
remotes[] (streamable-http, sse) |
-Inside the artifact — not surfaced in catalog | -
environmentVariables[] |
-Inside the artifact — not surfaced in catalog | -
_meta |
-Entry metadata for catalog-level hints; otherwise stays in artifact |
-
| (not in server.json) | -Entry publisher |
-
| (not in server.json) | -Entry trustManifest (identity, attestations, provenance) |
-
| (not in server.json) | -Entry tags for cross-artifact discovery |
-
| MCP Registry (centralized service) | -AI Catalog (decentralized, any URL) | -
The server.json format and AI Catalog address different concerns:
This separation means the AI Catalog entry is thin — it points at the
-server.json and adds only what server.json lacks: publisher
-identity, trust verification, and cross-ecosystem discoverability.
An MCP server listed in the Registry maps to a Catalog Entry whose
-url points to the server.json document and whose type
-reflects the Registry format:
{
- "identifier": "urn:air:anonymous.modelcontextprotocol.io:mcp:brave-search",
- "version": "1.0.2",
- "type": "application/mcp-server-card+json",
- "url": "https://registry.modelcontextprotocol.io/servers/brave-search/server.json",
- "description": "MCP server for Brave Search API integration",
- "tags": ["search", "brave", "web"],
- "publisher": {
- "identifier": "did:web:modelcontextprotocol.io",
- "displayName": "Model Context Protocol"
- },
- "trustManifest": {
- "identity": "did:web:anonymous.modelcontextprotocol.io:mcp:brave-search",
- "attestations": [
- {
- "type": "publisher-identity",
- "uri": "https://registry.modelcontextprotocol.io/certs/publisher.jwt",
- "description": "Verifies did:web:modelcontextprotocol.io as publisher"
- }
- ],
- "provenance": [
- {
- "relation": "publishedFrom",
- "sourceId": "https://github.com/modelcontextprotocol/servers",
- "registryUri": "https://registry.npmjs.org"
- }
- ]
- },
- "metadata": {
- "repository": "https://github.com/modelcontextprotocol/servers"
- },
- "updatedAt": "2026-03-15T10:00:00Z"
-}
-The url points to the complete server.json. A client fetches the
-catalog entry for discovery and trust evaluation, then retrieves the
-server.json for operational details (packages, transports, env vars).
--Note: This example uses
-application/jsonbecause the MCP -Registry has not registered a dedicated media type forserver.json. -When referencing an MCP Server Card (SEP-1649) instead, use -application/mcp-server-card+json— see -Relationship to MCP Server Cards.
The MCP Registry — a centralized index of MCP servers — can be
-represented as an AI Catalog. This enables clients that understand
-application/ai-catalog+json to discover MCP servers alongside A2A
-agents, skills, and other artifacts:
{
- "specVersion": "1.0",
- "host": {
- "displayName": "MCP Server Registry",
- "identifier": "did:web:modelcontextprotocol.io",
- "documentationUrl": "https://modelcontextprotocol.io/docs"
- },
- "entries": [
- {
- "identifier": "urn:air:anonymous.modelcontextprotocol.io:mcp:brave-search",
- "version": "1.0.2",
- "type": "application/mcp-server-card+json",
- "url": "https://registry.modelcontextprotocol.io/servers/brave-search/server.json",
- "description": "MCP server for Brave Search API integration",
- "tags": ["search", "brave"]
- },
- {
- "identifier": "urn:air:modelcontextprotocol.github.io:mcp:filesystem",
- "version": "1.0.2",
- "type": "application/mcp-server-card+json",
- "url": "https://registry.modelcontextprotocol.io/servers/filesystem/server.json",
- "description": "MCP server for filesystem operations",
- "tags": ["filesystem", "files"]
- },
- {
- "identifier": "urn:air:example.github.io:mcp:weather-mcp",
- "version": "0.5.0",
- "type": "application/mcp-server-card+json",
- "url": "https://registry.modelcontextprotocol.io/servers/weather/server.json",
- "description": "Python MCP server for weather data access",
- "tags": ["weather", "python"],
- "publisher": {
- "identifier": "did:web:example.github.io",
- "displayName": "Example Corp"
- }
- }
- ]
-}
-The MCP Registry is a centralized service. AI Catalog enables
-decentralized discovery: any domain can publish its MCP servers at
-/.well-known/ai-catalog.json without registering with a central
-authority.
A vendor hosting its own MCP servers can publish:
-https://api.acme-corp.com/.well-known/ai-catalog.json
-Clients and crawlers discover the catalog via the well-known URL,
-find entries by type, and fetch the referenced artifacts for
-operational details — whether those are MCP Server Cards, Registry
-server.json documents, or other AI artifact formats.
The centralized MCP Registry and decentralized AI Catalogs are -complementary. The registry can serve an AI Catalog as its response -format, while individual domains publish their own catalogs for -direct discovery.
-The server.json format has no trust or identity layer. AI Catalog
-fills this gap:
server.json.MCP Server Cards
-(SEP-1649)
-define a static discovery document for individual HTTP-based MCP
-servers at /.well-known/mcp/server-card.json. A Server Card mirrors
-the MCP initialization handshake response: it carries the server's
-name, version, transport configuration, capabilities, authentication
-requirements, and optionally the full list of tools, resources, and
-prompts.
An MCP Server Card is a static discovery document for an individual +HTTP-based MCP server, describing its identity and how to connect to it. +A Catalog Entry references the card wherever the server publishes it, as +in the examples below. See +SEP-2127 +for the Server Card's schema, fields, and hosting conventions.
+In AI Catalog terms, the Server Card is the artifact content — the
+native metadata that a Catalog Entry references via its url, declared
+with the known type application/mcp-server-card+json. The AI Catalog
+does not duplicate or redefine Server Card fields; it provides the
+discovery and trust layer that the Server Card does not address.
AI Catalog and MCP Server Cards address different layers of discovery:
The two mechanisms layer naturally. An AI Catalog entry for an MCP -server can reference the Server Card as its artifact content:
+| MCP Server Card | +AI Catalog Equivalent | +
|---|---|
| Server Card document (whole file) | +Artifact content via entry url (type application/mcp-server-card+json) or data |
+
Server name (reverse-DNS identifier) |
+Entry identifier (mapped to the urn:air:{publisher}:{namespace}:{name} URN form — e.g. urn:air:example.com:mcp:finance-server) |
+
title |
+Stays in the Server Card (which carries its own title); entry displayName is omitted unless the artifact lacks a name |
+
description |
+Entry description |
+
version |
+Entry version |
+
| transport / capabilities / tools / resources / auth | +Inside the Server Card — not surfaced in the catalog | +
repository |
+Entry metadata.repository |
+
| (not in the Server Card) | +Entry publisher |
+
| (not in the Server Card) | +Entry trustManifest (identity, attestations, provenance) |
+
| (not in the Server Card) | +Entry tags for cross-artifact discovery |
+
A remote MCP server maps to a Catalog Entry whose url points to the
+server's Server Card and whose type is the known type
+application/mcp-server-card+json:
{
"identifier": "urn:air:example.com:mcp:finance-server",
+ "version": "1.0.2",
"type": "application/mcp-server-card+json",
- "url": "https://api.acme-corp.com/.well-known/mcp/server-card.json",
+ "url": "https://api.acme-corp.com/mcp/server-card",
"description": "MCP server for financial data and trading tools",
"tags": ["finance", "mcp"],
"publisher": {
@@ -2097,11 +1922,74 @@
}
}
++Note on
+type: Thetypemember is an open-text type identifier +(ADR 0014); +any string is accepted, with a recommended set of "known types." The +known type for an MCP server referenced by its Server Card is +application/mcp-server-card+json. Note the deliberate naming +distinction: the MCP Server Card extension uses +application/mcp-server-card+json(notapplication/mcp-server+json) +to avoid colliding with the MCP Registry'sserver.jsonconcept +(modelcontextprotocol/experimental-ext-server-card issue #9 / PR #18).
A domain that hosts remote MCP servers can publish them as an AI Catalog,
+letting clients that understand application/ai-catalog+json discover
+those servers alongside A2A agents, skills, and other artifacts. Each
+entry points to a server's Server Card:
{
+ "specVersion": "1.0",
+ "host": {
+ "displayName": "Acme MCP Servers",
+ "identifier": "did:web:acme-corp.com",
+ "documentationUrl": "https://acme-corp.com/docs"
+ },
+ "entries": [
+ {
+ "identifier": "urn:air:acme-corp.com:mcp:finance-server",
+ "version": "1.0.2",
+ "type": "application/mcp-server-card+json",
+ "url": "https://api.acme-corp.com/finance/server-card",
+ "description": "MCP server for financial data and trading tools",
+ "tags": ["finance", "mcp"]
+ },
+ {
+ "identifier": "urn:air:acme-corp.com:mcp:docs-search",
+ "version": "1.0.2",
+ "type": "application/mcp-server-card+json",
+ "url": "https://api.acme-corp.com/docs-search/server-card",
+ "description": "MCP server for searching internal documentation",
+ "tags": ["search", "docs"]
+ },
+ {
+ "identifier": "urn:air:acme-corp.com:mcp:ci-cd",
+ "version": "0.5.0",
+ "type": "application/mcp-server-card+json",
+ "url": "https://api.acme-corp.com/ci-cd/server-card",
+ "description": "MCP server for CI/CD pipeline operations",
+ "tags": ["ci", "cd", "devops"]
+ }
+ ]
+}
+AI Catalog enables decentralized discovery: any domain can publish its
+MCP servers at /.well-known/ai-catalog.json without registering with a
+central authority.
A vendor hosting its own MCP servers can publish:
+https://api.acme-corp.com/.well-known/ai-catalog.json
+A client discovering MCP servers follows this flow:
/.well-known/ai-catalog.json to discover all artifacts on
a domain (MCP servers, A2A agents, plugins, etc.).type to find MCP servers.type (application/mcp-server-card+json) to find
+ MCP servers.url for operational details
(transport, capabilities, tools, authentication).A Server Card describes a single server but has no cross-server discovery +or trust layer. AI Catalog fills this gap:
+