FlatBuffers is a free software library implementing a serialization format similar to Protocol Buffers, Thrift, Apache Avro, SBE, and Cap'n Proto, primarily written by Wouter van Oortmerssen and open-sourced by Google.

It supports “zero-copy” deserialization, so that accessing the serialized data does not require first copying it into a separate part of memory.

Unlike Protocol Buffers, which uses variable length integers, FlatBuffers encodes integers in their native size, which favors performance but leads to longer encoded representations.

FlatBuffers can be used in software written in C++, C#, C, Go, Java, JavaScript, Kotlin, Lobster, Lua, PHP, Python, Rust, Swift, and TypeScript.

The schema compiler runs on Android, Microsoft Windows, macOS, and Linux,[3] but games and other programs use FlatBuffers for serialization work on many other operating systems as well, including iOS, Amazon's Fire OS, and Windows Phone.