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Protobuf Formatter

Format and pretty-print .proto (Protocol Buffers) source — consistent indentation, blank-line spacing between messages/enums/services, aligned enum values, and optional sorting of fields by tag number. Includes basic syntax validation. Runs entirely in your browser.

Input

Output

Formatted protobuf
Validation
Issue
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Guides

Paste inconsistently indented .proto source and get back a cleanly formatted Protocol Buffers schema — consistent indentation, blank lines between messages/enums/services, aligned enum values, and an optional sort of fields by tag number. A quick validation pass flags unbalanced braces, an unterminated string or comment, and a missing syntax declaration. Everything runs locally in your browser.

How to use it

  1. Paste your .proto file content.
  2. Choose 2 spaces or 4 spaces for indentation.
  3. Turn on Sort fields by tag number to reorder each message's fields by their tag number (comments stay attached to the field they preceded) — leave it off to keep your original field order.
  4. Check the Validation panel for any syntax issues, and copy or download the formatted result.

What it formats

  • syntax, package, import and top-level option statements, grouped and ordered at the top of the file.
  • message bodies, including nested messages, oneof blocks, map<K, V> fields, reserved and extensions statements.
  • enum bodies, with every value's = aligned to the longest name in that enum.
  • service bodies, with each rpc method (including stream request/response and inline rpc options) on its own block, separated by a blank line.
  • Line (//) and block (/* */) comments — both standalone and attached to the statement they lead or trail.

Does it validate the schema semantically?

No — this checks syntax, not schema semantics. It won't catch a duplicate field tag number, an undefined message type reference, or an incompatible field type change; it flags structural problems (unbalanced braces, an unterminated string/comment) and a missing syntax = "proto2"|"proto3" declaration. For real compilation, use protoc or your language's protobuf compiler.

Is my schema uploaded anywhere?

No. Tokenizing, parsing and formatting all run locally in your browser; your .proto source is never sent to a server.

Need to work with protobuf data instead of the schema file?

Use the Protobuf Text ↔ JSON Converter to convert prototext to JSON and back. For other schema/config formats, see the GraphQL Schema Formatter or the SQL Formatter.

protobufprotogrpcformatterdeveloper

Use it from code

From 3 credits per call

REST API

curl -X POST https://api.iotools.cloud/v1/tool/protobuf-formatter \
  -H "Authorization: Bearer YOUR_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "protobufInput": "syntax = \"proto3\";\n\nmessage User {\n    string id…",
    "indentSize": "2",
    "sortFields": ""
  }'

Swap in your own key from your account. The tool's fields are the body — no wrapper.

Ask an AI agent

Use the IOTools `protobuf-formatter` tool (Protobuf Formatter) on this input:

YOUR_INPUT_HERE

Paste this at any agent connected to the IOTools MCP server, then add your input.

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