Match client requirements to the protocol version

Client capabilities and their settings change across MCP protocol versions. Check each declared requirement against every version in the primitive’s effective scope. Split variants when a requirement cannot be represented consistently across that scope.

Requirement

Each client capability requirement and nested member exists in every applicable protocol version’s ClientCapabilities type, with object values and a boolean listChanged.

Details

Rule ID: mcp.client-capabilities.protocol-shape
Owner: mcp
Surface: ClientCapabilities · Path: clientRequirements
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, Section 8.5
  • 8. Capabilities: req-client-requirements-protocol-version-valid
  • 8. Capabilities: req-client-requirements-values
  • 8. Capabilities: req-client-requirements-extensions

Based on

• Tier 1 — MCP schema.ts and normative specification text: MCP 2024-11-05 to 2026-07-28 schema.ts, interface ClientCapabilities (members and nested members per protocol version)
  • validation/mcp-schemas/2024-11-05/schema.ts#L182-L203
  • validation/mcp-schemas/2025-03-26/schema.ts#L202-L223
  • validation/mcp-schemas/2025-06-18/schema.ts#L224-L251
  • validation/mcp-schemas/2025-11-25/schema.ts#L305-L379
  • validation/mcp-schemas/2026-07-28/schema.ts#L711-L786

Examples

Valid example

Source: expected-valid/client-capability-requirements.json · Selected: /tools/0/clientRequirements

{
  "tasks": {
    "requests": {
      "sampling": {
        "createMessage": {}
      }
    }
  }
}

Invalid example

Source: expected-invalid/protocol-version-incompatible-client-capability-requirements.json · Selected: /tools/0/clientRequirements

{
  "tasks": {
    "list": {}
  }
}

Invalid example

Source: expected-invalid/invalid-client-requirement-value.json · Selected: /tools/0/clientRequirements/roots

{
  "listChanged": "yes"
}

Rule Source Code

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