Use content blocks supported by each protocol version

Tool and Prompt examples carry native MCP content, whose types and fields vary by protocol version. Check each block against the containing declaration’s full effective scope. A block valid in a newer version is not automatically valid in an older one.

Requirement

Content blocks in example results use only content types and fields the applicable protocol version defines: audio from MCP 2025-03-26, resource links and block _meta from 2025-06-18, and resource-link icons from 2025-11-25.

Details

Rule ID: mcp.content-block.protocol-version
Owner: mcp
Surface: ContentBlock
Kind: structural
Requirement level: must
Status: internal · Enforcement: internal

Protocol version applicability

`2024-11-05`	`2025-03-26`	`2025-06-18`	`2025-11-25`	`2026-07-28`
applies	applies	applies	applies	applies

Required by

MCP Description 0.9.0, Sections 9.3 and 11.3
- 9. Tools: req-tool-example-content-protocol-version
- 1. Prompts: req-prompt-example-content-protocol-version

Based on

Tier 1 — MCP schema.ts and normative specification text: MCP 2024-11-05 schema.ts, TextContent, ImageContent, and EmbeddedResource (no AudioContent, no ResourceLink, no content _meta)
Tier 1 — MCP schema.ts and normative specification text: MCP 2025-03-26 schema.ts, AudioContent
- validation/mcp-schemas/2025-03-26/schema.ts#L987-L1009
Tier 1 — MCP schema.ts and normative specification text: MCP 2025-06-18 schema.ts, ResourceLink and ContentBlock, _meta on content types
- validation/mcp-schemas/2025-06-18/schema.ts#L753-L762
- validation/mcp-schemas/2025-06-18/schema.ts#L1130-L1134
Tier 1 — MCP schema.ts and normative specification text: MCP 2025-11-25 schema.ts, Resource extends Icons (inherited by ResourceLink)
- validation/mcp-schemas/2025-11-25/schema.ts#L797-L838

Notes

The same diagnostic codes also report embedded resource _meta (mcp.resource-contents.meta.protocol-version) and annotations.lastModified (mcp.annotations.last-modified.protocol-version); the rule property identifies which.

Examples

Invalid example

Source: expected-invalid/protocol-version-incompatible-tool-example.json · Selected: /tools/0/examples/future-result/result/content/0

{
  "type": "resource_link",
  "uri": "resource://example/item",
  "name": "Future resource link"
}

Invalid example

Source: expected-invalid/invalid-prompt-example-semantics.json · Selected: /prompts/4/examples/resource-link-too-new/result/messages/0/content

{
  "type": "resource_link",
  "uri": "briefing://example",
  "name": "Example"
}

Rule Source Code

content.yaml at immutable tag v0.9.0-rc.3.