MessageDefinition resource (FHIR R4)

MessageDefinition is the FHIR R4 resource for defines the characteristics of a message that can be shared between systems, including the type of event that initiates the message, the content to be transmitted and what response(s), if any, are permitted.

Resource	MessageDefinition
FHIR version	R4 (4.0.1)
Canonical URL	http://hl7.org/fhir/StructureDefinition/MessageDefinition
Required elements	status (1..1), date (1..1), event[x] (1..1)

Example

{
  "resourceType": "MessageDefinition",
  "id": "messagedefinition-3d532841f9d92cb4eb026e9565306899",
  "status": "draft",
  "date": "2026-07-01T12:00:00Z",
  "eventCoding": {
    "system": "http://example.org/pidgeon/synthetic"
  }
}

Generated by the Pidgeon engine: pidgeon generate MessageDefinition --seed 20260722.

Validation context

strict pidgeon validate grades a MessageDefinition instance against the base R4 structure definition: missing required elements raise REQUIRED_FIELD_MISSING and cardinality violations raise CARDINALITY_MIN or CARDINALITY_MAX.(REQUIRED_FIELD_MISSING)

This answer, in your terminal

pidgeon lookup MessageDefinition

Wire it into your AI agent:

claude mcp add pidgeon -- npx -y @pidgeonhealth/mcp

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