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Protobuf Inspector Online — Free .proto File Parser Tool

Protobuf Inspector

Parse and inspect Protocol Buffer .proto files — view message structures, field types, enums, and services.

Free online Protobuf Inspector. Paste any .proto file and instantly explore its message definitions, field types and numbers, enums, nested messages, oneofs, and gRPC service/RPC definitions. Supports proto2 and proto3 syntax. Export the inspection output as a readable tree, JSON, Markdown documentation, or a flat table. Runs entirely in your browser — no data is sent to a server.

Keywords: protobuf inspector, proto file parser, protobuf viewer online, .proto file analyzer, protobuf schema viewer, proto3 inspector, grpc proto inspector, protobuf message fields, proto file online viewer, protocol buffer inspector, protobuf to json schema, inspect .proto file

Tags: protobuf, proto, grpc, schema, inspector, parser, api

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How to Protobuf Inspector Online

  1. Paste the contents of your .proto file into the input panel on the left, or upload the file directly.

  2. Click "Inspect" or press ⌘↵ to parse the Protobuf schema and extract all definitions.

  3. Browse the message tree in the output panel — expand messages to view nested fields, types, and field numbers.

  4. Switch between tabs to inspect Messages, Enums, Services/RPCs, and Options independently.

  5. Export the parsed schema as a JSON structure, Markdown documentation, or a field reference table using the export buttons.

Protobuf Inspector Features

  • Parses both proto2 and proto3 syntax, detecting the syntax declaration automatically

  • Extracts all message definitions with field names, types, field numbers, and labels (optional/required/repeated)

  • Displays enum definitions with all value names and their integer mappings

  • Lists gRPC service definitions and RPC methods with request/response message types and streaming flags

  • Handles nested message and enum definitions with proper scoping

  • Resolves oneof field groups and displays them with their member fields

  • Shows file-level and message-level options (e.g., java_package, go_package, deprecated)

  • Exports schema as JSON for programmatic processing or further tooling

  • Exports as Markdown documentation for API docs, wikis, or README files

  • Generates a tabular field reference with type, number, label, and description columns

  • Runs entirely in your browser — your .proto files are never uploaded to any server

  • Keyboard shortcut ⌘↵ to parse, ⌘⇧C to copy current export

Frequently Asked Questions

What is a .proto file?
A .proto file is a Protocol Buffers schema file that defines the structure of serialized data. It specifies message types (similar to structs or classes), field names and types, field numbers (used in the binary encoding), enumerations, and — for gRPC — service and RPC definitions. The .proto file is the source of truth compiled into language-specific code.
What is the difference between proto2 and proto3?
Proto3 is the current recommended version. It removes the required field label, makes all singular fields optional by default (with implicit zero values), adds the map field type natively, and removes default value declarations. Proto2 supports required/optional/repeated explicitly, allows custom default values, and uses extensions. Proto3 is preferred for new projects.
What information is extracted from the .proto file?
The inspector extracts: message definitions (with all fields, types, field numbers, and labels), enum definitions (with all symbolic names and integer values), service definitions (with RPC methods, request/response types, and client/server streaming flags), oneof groups, nested type definitions, and file-level and type-level options.
Can I validate .proto file syntax with this tool?
The inspector performs structural parsing and will report syntax errors if the .proto file is malformed. However, it does not perform semantic validation (such as checking that referenced message types actually exist). For full validation, use `protoc --proto_path=. --descriptor_set_out=/dev/null your.proto`.
What export formats are available?
Three export formats are available: (1) JSON — a structured object tree of all definitions for programmatic use, (2) Markdown — formatted documentation suitable for wikis, GitHub READMEs, or API docs, (3) Table — a flat CSV/TSV-style field reference listing message, field name, type, number, and label for every field in the schema.
How can I decode a binary Protobuf message?
This tool inspects .proto schema files — it does not decode binary Protobuf payloads. To decode binary Protobuf data, use `protoc --decode` with the message type and .proto file, or use a tool like protoscope, buf curl, or the gRPC reflection API. DevFlow's Protobuf Decoder tool can decode binary payloads if you have the .proto schema.
Is my .proto file safe to paste here?
Yes. All parsing runs locally in your browser — your schema is never transmitted to any server. This is safe even for internal or proprietary API schemas.

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