Is my JSON data uploaded to a server?

No. The conversion runs entirely in your browser with JavaScript. Nothing is sent over the network, which makes the tool safe for sensitive data.

How are field numbers assigned?

Field numbers are assigned sequentially within each message, and field names are converted to snake_case as recommended by the proto3 style guide.

What happens with null values or mixed arrays?

They are typed as google.protobuf.Value, and the struct.proto import is emitted only when this type is actually used.

JSON to Protobuf (proto3) Converter

JSON to Protobuf (proto3) Converter — Free Online Tool

Convert JSON to proto3 message definitions instantly in your browser. Free, private and offline-friendly: your data never leaves your device.

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Root name

JSON input

Protobuf output

Why convert JSON to Protobuf?

Writing .proto files by hand for an existing JSON payload is tedious. Paste a sample JSON document above and get ready-to-use proto3 message definitions in milliseconds, with one message per nested object.

How it works

The converter parses your JSON locally and emits proto3 messages with snake_case field names and sequential field numbers per message. Null values and heterogeneous arrays fall back to google.protobuf.Value, and the struct.proto import is included only if it is needed.

Frequently asked questions

Is my JSON data uploaded to a server?: No. The conversion runs entirely in your browser with JavaScript. Nothing is sent over the network, which makes the tool safe for sensitive data.
How are field numbers assigned?: Field numbers are assigned sequentially within each message, and field names are converted to snake_case as recommended by the proto3 style guide.
What happens with null values or mixed arrays?: They are typed as google.protobuf.Value, and the struct.proto import is emitted only when this type is actually used.