Keep completion result members within MCP fields

The nested completion object is closed even when its surrounding result is open. It accepts values, total, and hasMore, not arbitrary pagination or vendor fields. Remove additional members or explicitly review a different metadata destination.

Requirement

The completion object of a completion result contains only values, total, and hasMore.

Details

Rule ID: mcp.completion.result-closed
Owner: mcp
Surface: CompleteResult · Path: completion
Kind: structural
Requirement level: must
Protocol versions: independent of the MCP protocol version
Document schema locations: #/$defs/completionResult
Status: internal · Enforcement: internal

Required by

• MCP Description 0.9.0, Sections 10.4.6 and 11.4
  • 3. Document Structure: req-carried-nested-closed
  • 3. Document Structure: req-carried-closed-reject

Based on

• Tier 1 — MCP schema.ts and normative specification text: MCP 2024-11-05 to 2026-07-28 schema.ts, interface CompleteResult, completion (no index signature)
  • validation/mcp-schemas/2024-11-05/schema.ts#L974-L992
  • validation/mcp-schemas/2025-03-26/schema.ts#L1115-L1133
  • validation/mcp-schemas/2025-06-18/schema.ts#L1342-L1362
  • validation/mcp-schemas/2025-11-25/schema.ts#L2037-L2057
  • validation/mcp-schemas/2026-07-28/schema.ts#L2633-L2661

Examples

Valid example

Source: expected-valid/named-completion-examples.json · Selected: /resourceTemplates/0/completionExamples

{
  "issue-prefix": {
    "argument": {
      "name": "issue",
      "value": "12"
    },
    "result": {
      "completion": {
        "values": [
          "120",
          "121",
          "129"
        ],
        "hasMore": true,
        "total": 14
      }
    }
  }
}

Invalid example

Source: expected-invalid/completion-result-extra-field.json · Selected: /resourceTemplates/0/completionExamples/issue-prefix/result/completion

{
  "values": [
    "120",
    "121"
  ],
  "acmeRank": 1
}

Rule Source Code

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