Change validation

Occasionally, a user wants to validate an intended change to see what the result will be before actually making the change. For example, a request to provision new servers in a fleet will have an impact on the overall fleet size and cost, and could potentially have unexpected downstream effects.


APIs may provide an option to validate, but not actually execute, a request, and provide the same response (status code, headers, and response body) that it would have provided if the request was actually executed.

To provide this option, the method should include a bool validate_only field in the request message:

message ReviewBookRequest {
  string name = 1 [(google.api.resource_reference) = {
    type: ""
  int32 rating = 2;
  string comment = 3;

  // If set, validate the request and preview the review, but do not actually
  // post it.
  bool validate_only = 4;

The API must perform permission checks and any other validation that would be performed on a "live" request; a request using validate_only must fail if it determines that the actual request would fail.

Note: It may occasionally be infeasible to provide the full output. For example, if creating a resource would create an auto-generated ID, it does not make sense to do this on validation. APIs should omit such fields on validation requests in this situation.

Declarative-friendly resources


A resource that is declarative-friendly (AIP-128) must include a validate_only field on methods that mutate the resource.


  • 2020-10-06: Added declarative-friendly resource requirement.