MCP Server Cards (SEP-2127) vs AI Catalog well-known file
The map lists them as complementary: sites and agents commonly implement both.
| MCP Server Cards (SEP-2127) Server Card | 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 (superseded question -- see ard) |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://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 (superseded question -- see ard)” and you accept its maturity: status "Deprecated predecessor path of the ARD manifest", implementation shipping (agenticweb.wiki /check/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 It is no longer maintained; prefer its successor.
Read the full articles
- MCP Server Cards (SEP-2127): How can a client learn what an MCP server offers before connecting to it?
- AI Catalog well-known file: Which AI-capable artifacts and registries does this domain publish? (superseded question -- see ard)
mcp-server-cards.json · ai-catalog-well-known-file.json · Markdown