The Value Type

google.protobuf.Value and google.protobuf.Struct cover data that isn't a Protobuf message at all, just arbitrary JSON you don't want to model up front. Any, by contrast, carries a Protobuf message whose type isn't known until runtime.

A Value can be a null, a number, a string, a boolean, a struct of further values, or a list of them. Those six cases are exactly JSON's own types: null, number, string, boolean, object, and array.

A field typed as Value or Struct has no schema checking, so generated code can't tell you what's inside. Keep them for the places that need them, such as integrating with a schemaless NoSQL database or passing along a metadata blob nobody wants to write a schema for.

Any, Value, and Struct all fall under Well-Known Types. The Types reference lists the rest, including Timestamp and Duration.

Compare with a schema field: here the names theme, retries, and beta are all in the payload.

schema.proto

edition = "2024";

package demo.v1;

import "google/protobuf/struct.proto";

message Config {
  google.protobuf.Struct settings = 1;
}

Input JSON (editable)

{
  "settings": {
    "theme": "dark",
    "retries": 3,
    "beta": true
  }
}

ProtoJSON

Compiling the schema...

Editions

What Protobuf editions are, how they replace proto2 and proto3 syntax, and how features migrate schemas incrementally without breaking the wire format.

The Any Type

Editions