JSON Schema to Protobuf Converter
Paste an actual JSON Schema document to instantly generate a matching Protocol Buffers .proto message definition, with nested messages and sequential field numbers. Free online developer tool.
Paste a JSON Schema document
Protocol Buffers (.proto)
Protobuf message definitions will appear here...
Free JSON Schema to Protocol Buffers Converter
Paste an actual JSON Schema document — not a plain JSON data sample — to instantly generate a matching Protocol Buffers .proto message definition. Nested objects become nestedmessage definitions, arrays become repeated fields, and every field gets a sequential field number starting at 1.
How to Use It
Paste a draft-07-style JSON Schema object into the input box, or click "Load Example Schema" to see a sample run. The tool converts your schema's type/properties/items keywords, then emits a proto3message block, numbering fields in the order they appear and nesting sub-messages inside their parent message body.
Example
Given a schema with properties: { name: { type: "string" }, tags: { type: "array", items: { type: "string" } } }, the tool generates message Root { string name = 1; repeated string tags = 2; }, with field numbers assigned in property order.
Common Use Cases
- Bootstrapping a .proto message definition for a gRPC service from an existing JSON Schema.
- Migrating a REST API's JSON Schema contract toward a Protocol Buffers-based service.
- Getting a first-draft .proto file to refine field numbering and types for by hand.
- Comparing how a JSON Schema's field types map onto Protobuf's scalar type system.
FAQs
How are JSON Schema types mapped to Protobuf types?
string maps to Protobuf's string, integer maps toint64, number maps to double, and boolean maps tobool. Fields with an unrecognized type fall back to string.
Are field numbers stable if I reorder my schema's properties?
No — field numbers are assigned sequentially in the order properties appear in your schema. If you reorder properties after generating a message once already in production use, you'll break wire compatibility, so treat the generated numbers as a starting point to lock in, not something to regenerate on every schema change.
Is my schema uploaded anywhere?
No — parsing and message generation happen entirely client-side in your browser. Nothing you paste is sent to a server.