Use MCP primitive schemas in elicitation forms

A form-mode requestedSchema is a flat object whose properties are MCP primitive schemas: string, number, integer, boolean, or enumeration, with only the keywords MCP defines for them.

Requirement

requestedSchema is an object schema of MCP primitive property schemas with their defined keywords only.

Details

Rule ID: mcp.elicitation.form-schema.members
Owner: mcp
Surface: ElicitRequest requestedSchema
Kind: structural
Requirement level: must
Protocol versions: independent of the MCP protocol version
Document schema locations: #/$defs/elicitationFormSchema, #/$defs/elicitationFormProperty, #/$defs/elicitationFormOption
Status: internal · Enforcement: internal

Required by

• MCP Description 0.9.0, Section 12.3
  • 12. Elicitation Declarations: req-elicitation-form-shape

Based on

• Tier 1 — MCP schema.ts and normative specification text: MCP 2025-11-25 and 2026-07-28 schema.ts, ElicitRequestFormParams and PrimitiveSchemaDefinition
  • validation/mcp-schemas/2025-11-25/schema.ts#L2155-L2178
  • validation/mcp-schemas/2025-11-25/schema.ts#L2234-L2235
  • validation/mcp-schemas/2026-07-28/schema.ts#L2788-L2811
  • validation/mcp-schemas/2026-07-28/schema.ts#L2867-L2868

Examples

Invalid example

Source: expected-invalid/component-contextual-schemas.json · Selected: /tools/0/elicitations/0/requestedSchema

{
  "$componentRef": "#/components/schemas/NestedForm"
}

Rule Source Code

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