docker-compose/compose/config/service_schema.json

{
  "$schema": "http://json-schema.org/draft-04/schema#",
  "id": "service_schema.json",

  "type": "object",

  "allOf": [
    {"$ref": "fields_schema.json#/definitions/service"},
    {"$ref": "#/definitions/constraints"}
  ],

  "definitions": {
    "constraints": {
      "id": "#/definitions/constraints",
      "anyOf": [
        {
          "required": ["build"],
          "not": {"required": ["image"]}
        },
        {
          "required": ["image"],
          "not": {"anyOf": [
            {"required": ["build"]},
            {"required": ["dockerfile"]}
          ]}
        }
      ]
    }
  }
}