msgspec

msgspec is a serialization and validation library for Python with built-in support for JSON, MessagePack, YAML, and TOML. It defines message schemas using ordinary Python type annotations and a Struct type, then encodes and decodes messages to and from those formats.

Decoding can validate input against the declared schema at the same time, catching type mismatches such as an integer where a string is expected. The project reports its JSON and MessagePack encoders and decoders as among the fastest available for Python, faster in combined encode-and-validate benchmarks than some libraries that only decode.

msgspec has no required dependencies and is distributed under the BSD license.