Use MCP content blocks and resource contents

Content in example results is an MCP content block selected by type: text, image, audio, resource link, or embedded resource. Resource contents have a uri and either text or blob. Each carries only the fields its MCP type defines.

Requirement

Content blocks and resource contents match exactly one MCP content type, with its required fields and no unknown fields.

Details

Rule ID: mcp.content.members
Owner: mcp
Surface: ContentBlock, ResourceContents
Kind: structural
Requirement level: must
Protocol versions: independent of the MCP protocol version
Document schema locations: #/$defs/toolResultContent, #/$defs/resourceContents
Status: internal · Enforcement: internal

Required by

• MCP Description 0.9.0, Section 3.6
  • 3. Document Structure: req-carried-defined-fields
  • 3. Document Structure: req-carried-closed-reject
  • 10. Resources and Resource Templates: req-resource-annotations-not-in-examples
  • 10. Resources and Resource Templates: req-resource-contents-fields

Based on

• Tier 1 — MCP schema.ts and normative specification text: MCP 2025-11-25 and 2026-07-28 schema.ts, ContentBlock and ResourceContents
  • validation/mcp-schemas/2025-11-25/schema.ts#L1740-L1741
  • validation/mcp-schemas/2025-11-25/schema.ts#L881-L897
  • validation/mcp-schemas/2026-07-28/schema.ts#L2305-L2306
  • validation/mcp-schemas/2026-07-28/schema.ts#L1514-L1527

Examples

Invalid example

Source: expected-invalid/discriminated-union-members.json · Selected: /tools/0/interactionExamples/invalid/result/content/0

{
  "type": "text",
  "tetx": "Done"
}

Rule Source Code

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