Match example results to every applicable version

A completed example result must contain the fields each applicable MCP protocol version requires, with valid values. Check the result’s full effective scope, not only the newest version. Fields permitted but undefined on open result types are handled separately as warnings.

Requirement

An example result contains every field that each applicable MCP protocol version requires, and every field a protocol version defines has a valid value.

Details

Rule ID: mcpdesc.example.result.protocol-fidelity
Owner: mcpdesc
Surface: Example result
Kind: mcpdesc-semantic
Requirement level: Not specified in the rule record
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, 10.4.4, 10.4.6, 11.3, and 11.4
  • 3. Document Structure: req-carried-defined-fields
  • 9. Tools: req-tool-example-result-shape
  • 10. Resources and Resource Templates: req-resource-example-result-shape
  • 11. Prompts: req-prompt-example-result-shape
• Examples fail fast decision (validation README, 2026-10-25, issue #72)
  • validation/README.md#examples-fail-fast

Based on

• Tier 1 — MCP schema.ts and normative specification text: MCP 2026-07-28 schema.ts, interface Result (resultType required) and interface CacheableResult (ttlMs, cacheScope required)
  • validation/mcp-schemas/2026-07-28/schema.ts#L218-L236
  • validation/mcp-schemas/2026-07-28/schema.ts#L1076-L1110

Notes

Fields an MCP protocol version does not define are governed by mcp.result.additional-properties.preserve (accepted with a warning). When present, resultType must be “complete”, ttlMs non-negative, and cacheScope “public” or “private” in every applicable protocol version (document schema).

Examples

Valid example

Source: expected-valid/named-tool-examples.json · Selected: /tools/0/examples

{
  "paris.complete": {
    "input": {
      "city": "Paris"
    },
    "result": {
      "resultType": "complete",
      "content": [
        {
          "type": "text",
          "text": "Paris: 21.5 C"
        },
        {
          "type": "image",
          "data": "aW1hZ2U=",
          "mimeType": "image/png"
        },
        {
          "type": "audio",
          "data": "YXVkaW8=",
          "mimeType": "audio/wav"
        },
        {
          "type": "resource",
          "resource": {
            "uri": "weather://paris/report",
            "mimeType": "text/plain",
            "text": "Clear"
          }
        },
        {
          "type": "resource_link",
          "uri": "weather://paris/map",
          "name": "Paris map",
          "mimeType": "image/png"
        }
      ],
      "structuredContent": {
        "temperature": 21.5
      },
      "isError": false
    }
  }
}

Valid example

Source: expected-valid/named-resource-examples.json · Selected: /resources/0/examples

{
  "two-files": {
    "result": {
      "contents": [
        {
          "uri": "file:///project/src/",
          "mimeType": "inode/directory",
          "text": "main.rs\nlib.rs\n"
        },
        {
          "uri": "file:///project/src/main.rs",
          "mimeType": "text/x-rust",
          "text": "fn main() {}\n",
          "_meta": {
            "captured": true
          }
        },
        {
          "uri": "file:///project/src/lib.rs",
          "mimeType": "text/x-rust",
          "text": "pub fn answer() -> u8 { 42 }\n"
        }
      ],
      "_meta": {
        "snapshot": "example"
      }
    }
  }
}

Valid example

Source: expected-warning/legacy-result-meta.json · Selected: /resources/0/examples/with-result-meta/result

{
  "contents": [
    {
      "uri": "test://legacy",
      "text": "legacy"
    }
  ],
  "_meta": {
    "trace": "r1"
  }
}

Valid example

Source: expected-warning/open-results-shared-across-protocol-versions.json · Selected: /tools/0/examples/paris/result

{
  "resultType": "complete",
  "content": [
    {
      "type": "text",
      "text": "Paris: 18 C"
    }
  ]
}

Invalid example

Source: expected-invalid/invalid-prompt-example-semantics.json · Selected: /prompts/0/examples/unknown-and-missing/result

{
  "messages": [
    {
      "role": "user",
      "content": {
        "type": "text",
        "text": "Summarize Paris."
      }
    }
  ]
}

Invalid example

Source: expected-invalid/invalid-completion-example-semantics.json · Selected: /prompts/3/completionExamples/missing-result-type/result

{
  "completion": {
    "values": [
      "Ada"
    ],
    "hasMore": false
  }
}

Rule Source Code

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