protoc

Protocol Buffers compiler and code generator

TLDR

Generate Python code from a .proto file

$ protoc --python_out=[path/to/output_directory] [input_file.proto]

Generate Java code from a .proto file that imports other .proto files

$ protoc --java_out=[path/to/output_directory] --proto_path=[path/to/import_search_path] [input_file.proto]

Generate code for multiple languages

$ protoc --csharp_out=[path/to/c#_output_directory] --js_out=[path/to/js_output_directory] [input_file.proto]

Encode a text-format message into a protocol message from a .proto file

$ protoc < [message.txt] --encode=[TypeName] [input_file.proto]

Decode a protocol message into text-format from a .proto file

$ protoc < [message.bin] --decode=[TypeName] [input_file.proto]

Decode a protocol message into raw tag/value pairs

$ protoc < [message.bin] --decode_raw

SYNOPSIS

protoc [--cpp_out=OUTDIR] [**--javaout=_OUT_DIR_] [--pythonout=**OUTDIR] [-IPATH | --proto_path=PATH] PROTOFILE_

protoc is the official compiler for Google's Protocol Buffers, a language-neutral serialization framework. It reads .proto definition files that describe structured data formats and generates language-specific source code for serializing and deserializing that data efficiently in C++, Java, Python, Go, and many other languages through plugins.
The compiler resolves imports between .proto files using search paths specified with -I (or --proto_path), and can generate code for multiple target languages in a single invocation. It also supports encoding and decoding protocol buffer messages on the command line for debugging and testing purposes.
protoc is a core component of the gRPC ecosystem, where .proto files define both data structures and service interfaces for remote procedure calls.

OPTIONS

-IPATH, --proto_path=PATH

Specify the directory in which to search for imports. May be specified multiple times; directories will be searched in order. If not given, the current working directory is used.

--cpp_out=OUTDIR_

Enable generation of C++ bindings and store them in OUTDIR_.

--java_out=OUTDIR_

Enable generation of Java bindings and store them in OUTDIR_.

--python_out=OUTDIR_

Enable generation of Python bindings and store them in OUTDIR_.

-h, --help

Show summary of options.

--version

Show version of program.

Note that at least one of the --cpp_out, --java_out and --python_out options must be given (otherwise the program has nothing to do). Its also possible to specify more than one.

CAVEAT

Finicky path resolution: it demands precise --proto_path (-I) flags for all .proto files and imports, often failing with "file not found" errors if paths aren't exactly matched (no smart relative/absolute equivalence). Always run from the proto root dir, include parent paths in -I, and consider wrappers like Buf for easier handling.

HISTORY

Initially developed internally at Google in 2001 as a way to handle structured data serialization more efficiently than XML, with the first public release occurring in 2008 under an open-source license. The protoc compiler itself evolved alongside, starting as a C++-based tool and expanding to support multiple languages like Java, Python, and Go through generated code stubs. Over the years, it has seen continuous updates, with version 3 introducing significant syntax changes in 2016 and recent iterations up to 2026 focusing on performance optimizations, nanoPB for embedded systems, and better integration with gRPC.