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{mcpdesc}

Use recognized client capability requirements

A primitive’s clientRequirements lists minimum client capabilities, not custom top-level names. Put custom requirements in experimental or in extensions where defined, after reviewing their meaning. Server capability advertisement and client requirements are different declarations.

Requirement

Section titled “Requirement”

A Client Capability Requirements Object names only client capabilities the applicable MCP protocol version defines; custom requirements go in experimental and, from MCP 2026-07-28, in extensions.

Details

Section titled “Details”

Rule ID: mcp.client-capabilities.members
Owner: mcp
Surface: ClientCapabilities · Path: clientRequirements
Kind: structural
Requirement level: must
Document schema locations: #/$defs/clientCapabilityRequirements, #/$defs/clientCapabilityValue
Status: arbitrated · Enforcement: internal

Protocol version applicability

Section titled “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

Section titled “Required by”

Based on

Section titled “Based on”

Gaps and arbitrations

Section titled “Gaps and arbitrations”

Examples

Section titled “Examples”

Valid example

Section titled “Valid example”

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

{
  "sampling": {
    "tools": {}
  },
  "experimental": {
    "com.example/review": {}
  }
}

Invalid example

Section titled “Invalid example”

Source: expected-invalid/unknown-client-capability-requirement.json · Selected: /tools/0/clientRequirements

{
  "acmeReplay": {}
}

Rule Source Code

Section titled “Rule Source Code”

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