SEP-2127: MCP Server Cards - HTTP Server Discovery changedseps/2127-mcp-server-cards
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1111> This SEP has reached Final status and is preserved as a historical record of
1212> the design as accepted. Changes made to the protocol after finalization are
1313> not reflected here. Refer to the [current
14> specification](/specification/latest.md) and its changelog for authoritative
14> specification](https://modelcontextprotocol.io/specification/latest.md) and its changelog for authoritative
1515> requirements.
1616
1717| Field | Value |
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3131
3232This SEP proposes adding a standardized, self-contained format to describe MCP servers for pre-connection discovery. This enables clients to automatically discover available transports, protocol versions, and connection guidance before establishing a connection.
3333
34As an Extensions Track SEP (per [SEP-2133](/seps/2133-extensions.md)), this document charters the **Server Card** extension and names its Working Group and maintainers. The detailed, normative wire format — the Server Card schema, field definitions, the discovery mechanics, and the full security analysis — is maintained in the [experimental-ext-server-card](https://github.com/modelcontextprotocol/experimental-ext-server-card) repository rather than inline here, following the precedent set by [SEP-1865 (MCP Apps)](/seps/1865-mcp-apps-interactive-user-interfaces-for-mcp.md).
34As an Extensions Track SEP (per [SEP-2133](https://modelcontextprotocol.io/seps/2133-extensions.md)), this document charters the **Server Card** extension and names its Working Group and maintainers. The detailed, normative wire format — the Server Card schema, field definitions, the discovery mechanics, and the full security analysis — is maintained in the [experimental-ext-server-card](https://github.com/modelcontextprotocol/experimental-ext-server-card) repository rather than inline here, following the precedent set by [SEP-1865 (MCP Apps)](https://modelcontextprotocol.io/seps/1865-mcp-apps-interactive-user-interfaces-for-mcp.md).
3535
3636## Motivation
3737
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9292and the discovery mechanics in [`docs/discovery.md`](https://github.com/modelcontextprotocol/experimental-ext-server-card/blob/main/docs/discovery.md)
9393are derived from it.
9494
95For purposes of SEP review, [extension repository snapshot `526201bb`](https://github.com/modelcontextprotocol/experimental-ext-server-card/tree/526201bbc80231daa40ffcdecfc9da4e54e5dc93) captures the contract considered by this proposal. After acceptance, implementers should follow the current, versioned extension specification rather than this historical snapshot. As defined by [SEP-2133](/seps/2133-extensions.md#iteration), extension maintainers may evolve the specification independently while preserving backward compatibility; breaking changes require a new extension identifier.
95For purposes of SEP review, [extension repository snapshot `526201bb`](https://github.com/modelcontextprotocol/experimental-ext-server-card/tree/526201bbc80231daa40ffcdecfc9da4e54e5dc93) captures the contract considered by this proposal. After acceptance, implementers should follow the current, versioned extension specification rather than this historical snapshot. As defined by [SEP-2133](https://modelcontextprotocol.io/seps/2133-extensions.md#iteration), extension maintainers may evolve the specification independently while preserving backward compatibility; breaking changes require a new extension identifier.
9696
9797At a high level, the Server Card extension introduces:
9898
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188188
189189## References
190190
191* [SEP-1865: MCP Apps (Extensions Track precedent)](/seps/1865-mcp-apps-interactive-user-interfaces-for-mcp.md)
192* [SEP-2133: Extensions](/seps/2133-extensions.md)
191* [SEP-1865: MCP Apps (Extensions Track precedent)](https://modelcontextprotocol.io/seps/1865-mcp-apps-interactive-user-interfaces-for-mcp.md)
192* [SEP-2133: Extensions](https://modelcontextprotocol.io/seps/2133-extensions.md)
193193* [RFC 8414: OAuth 2.0 Authorization Server Metadata](https://datatracker.ietf.org/doc/html/rfc8414)
194194* [RFC 8615: Well-Known URIs](https://datatracker.ietf.org/doc/html/rfc8615)
195195* [MCP Protocol Specification](https://modelcontextprotocol.io/specification)
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