# MCP Server Cards (SEP-2127) vs AI Catalog well-known file

The map lists them as complementary: sites and agents commonly implement both.

[1 Discover](/category/discover/) [MCP Server Cards (SEP-2127)](/protocols/mcp-server-cards/) · [1 Discover](/category/discover/) [AI Catalog well-known file](/protocols/ai-catalog-well-known-file/)

|  | [MCP Server Cards (SEP-2127)](/protocols/mcp-server-cards/) Server Card | [AI Catalog well-known file](/protocols/ai-catalog-well-known-file/) |
| --- | --- | --- |
| Lifecycle step | 1 Discover: What is here, and where? | 1 Discover: What is here, and where? |
| Answers | How can a client learn what an MCP server offers before connecting to it? | Which AI-capable artifacts and registries does this domain publish? (superseded question -- see ard) |
| Governed by | Model Context Protocol project (SEP process, MCP governance) | ARD / ards-project (see ard) |
| Status (issuer's words) | SEP-2127 Final (2026-10-06), Extensions Track charter; the MCP Registry working group page still describes Server Cards as experimental | Deprecated predecessor path of the ARD manifest |
| Version | SEP-2127 (Final) (2026-10-06) | n/a -- not a separately versioned artifact |
| Form / transport | document format | well-known file |
| Found at | GET <streamable-http-url>/server-card | /.well-known/ai-catalog.json |
| Implementation | multi-implementation | shipping — agenticweb.wiki /check/ probe (43/268 origins still serving the legacy /.well-known/ai-catalog.json path) |
| Evidence | 7 verified, 1 reported | 2 verified |
| Primary use case | Let agents discover my API or service | Let agents discover my API or service |
| Last verified | 2026-10-23 (current) | 2026-10-23 (current) |
| Specification | [https://github.com/modelcontextprotocol/modelcontextprotocol/blob/main/seps/2127-mcp-server-cards.md](https://github.com/modelcontextprotocol/modelcontextprotocol/blob/main/seps/2127-mcp-server-cards.md) | [https://raw.githubusercontent.com/ards-project/ard-spec/main/spec/ard.md](https://raw.githubusercontent.com/ards-project/ard-spec/main/spec/ard.md) |

## When to use which

- Choose MCP Server Cards (SEP-2127) when your question is “How can a client learn what an MCP server offers before connecting to it?” and you accept its maturity: status "SEP-2127 Final (2026-10-06), Extensions Track charter; the MCP Registry working group page still describes Server Cards as experimental", implementation multi-implementation.
- Choose AI Catalog well-known file when your question is “Which AI-capable artifacts and registries does this domain publish? (superseded question -- see ard)” and you accept its maturity: status "Deprecated predecessor path of the ARD manifest", implementation shipping (agenticweb.wiki /check/ probe (43/268 origins still serving the legacy /.well-known/ai-catalog.json path)). It is no longer maintained; prefer its successor.

Guidance is derived from the two records (question, status, implementation, prerequisites, pairings), not from opinion. Each record's page carries its numbered references.

## Read the full articles

- [MCP Server Cards (SEP-2127)](/protocols/mcp-server-cards/): How can a client learn what an MCP server offers before connecting to it?
- [AI Catalog well-known file](/protocols/ai-catalog-well-known-file/): Which AI-capable artifacts and registries does this domain publish? (superseded question -- see ard)

Ask the MCP server to compare any two: the compare-protocols prompt, or get on both ids. [Connect](/connect/).

[mcp-server-cards.json](/data/protocols/mcp-server-cards.json) · [ai-catalog-well-known-file.json](/data/protocols/ai-catalog-well-known-file.json) · [Markdown](/compare/mcp-server-cards-vs-ai-catalog-well-known-file/index.md)