Standard Options

Protobuf options control how code is generated and how data is mapped. They are categorized by scope: File, Message, Field, or Service. The full set of standard options is defined in descriptor.proto.

option go_package: Defines the Go import path.
option java_package: Defines the Java package.
option optimize_for = SPEED;: Generates highly optimized (but larger) code. Alternatives: CODE_SIZE, LITE_RUNTIME.
[deprecated = true]: Marks a field as deprecated.
[json_name = "custom"]: Sets a custom JSON key.

edition = "2024";

option go_package = "github.com/example/v1";
option java_package = "com.example.v1";
option optimize_for = SPEED;

message User {
  string user_id = 1 [json_name = "uid"];
  string old_field = 2 [deprecated = true];
}

JSON

{
  "uid": "01H8XGJWBWBAQ4",
  "oldField": "still serialized"
}

Unknown Fields

How Protobuf preserves fields a decoder doesn't recognize, why that keeps old clients compatible with new schemas, and where unknown fields can bite.

Editions

Unknown Fields