How are numbers typed?

Whole numbers become int64 and numbers with a decimal point become double. Change them to int32, uint32, float and so on if you need a different width.

What happens with null, empty arrays or nested arrays?

These map to google.protobuf.Value (and import "google/protobuf/struct.proto" is added), because proto3 has no native null and doesn't allow repeated repeated fields.

Why do some fields have a json_name option?

Proto field names are lower_snake_case. When the canonical camelCase JSON mapping wouldn't reproduce your original key, a [json_name = "..."] option is added so JSON round-trips correctly.

Is my JSON sent anywhere?

No. Conversion happens entirely in your browser; nothing is uploaded.

JSON to Protobuf Schema Converter (proto3)

Paste any JSON object or array and get a ready-to-use Protocol Buffers (proto3) schema, with fields mapped to proto scalar types (string, int64, double, bool), repeated fields for arrays, and separate messages for nested objects. Keys that aren't lower_snake_case get a [json_name = "..."] option so the canonical JSON mapping still matches your original key. Everything runs locally in your browser — your JSON is never uploaded.

—

Root message nameJSON input

Protobuf schema

syntax = "proto3";

message Message {
  int64 id = 1;
  string name = 2;
  bool active = 3;
  repeated string tags = 4;
  Profile profile = 5;
}

message Profile {
  string city = 1;
  string created_at = 2;
}

How to use

Paste or type your JSON into the input box.
Optionally rename the root message (defaults to Message).
Copy the generated .proto schema from the output box.

Frequently asked questions

How are numbers typed?: Whole numbers become int64 and numbers with a decimal point become double. Change them to int32, uint32, float and so on if you need a different width.
What happens with null, empty arrays or nested arrays?: These map to google.protobuf.Value (and import "google/protobuf/struct.proto" is added), because proto3 has no native null and doesn't allow repeated repeated fields.
Why do some fields have a json_name option?: Proto field names are lower_snake_case. When the canonical camelCase JSON mapping wouldn't reproduce your original key, a [json_name = "..."] option is added so JSON round-trips correctly.
Is my JSON sent anywhere?: No. Conversion happens entirely in your browser; nothing is uploaded.

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