Legacy HTTP plus SSE remains representable but is deprecated for later MCP protocol versions. The warning does not by itself invalidate the document. Review whether the server still offers that transport or whether the description should advertise Streamable HTTP instead.
Requirement
Section titled “Requirement”Legacy HTTP+SSE associated with MCP 2025-03-26 or later is reported, because Streamable HTTP replaces it.
Details
Section titled “Details”Rule ID: mcp.transport.legacy-sse.deprecated
Owner: mcp
Surface: Transport
Kind: semantic
Requirement level: should
Status: internal · Enforcement: internal
Protocol version applicability
Section titled “Protocol version applicability”2024-11-05 |
2025-03-26 |
2025-06-18 |
2025-11-25 |
2026-07-28 |
|---|---|---|---|---|
| not-applicable | applies | applies | applies | applies |
Required by
Section titled “Required by”- MCP Description 0.9.0, Section 6.2
- 6. Transports: req-transport-legacy-sse-warning
Based on
Section titled “Based on”- Tier 1 — MCP schema.ts and normative specification text: MCP 2025-03-26 specification, Basic, Transports, Backwards Compatibility (deprecated HTTP+SSE transport)
Examples
Section titled “Examples”Accepted with a warning
Section titled “Accepted with a warning”Source: expected-warning/legacy-sse-modern-protocol-version.json · Selected: /transports/0
{ "type": "sse", "url": "https://example.com/sse"}Rule Source Code
Section titled “Rule Source Code”transport.yaml at immutable tag v0.9.0-rc.3.