jcrist/msgspec

msgspec is a Python library for converting data between Python objects and common data formats: JSON, MessagePack, YAML, and TOML. Its main selling point is speed. According to the benchmarks linked in the README, its JSON and MessagePack implementations are the fastest available for Python, and it can decode and validate JSON faster than some libraries can decode JSON alone. The library works by letting you define your data shapes using standard Python type annotations. You create a Struct (a lightweight alternative to Python's built-in dataclasses) that describes what fields a piece of data should have and what types they should be. When you decode incoming data into that Struct, msgspec automatically checks that the values match the expected types and raises a clear error with a precise location if something does not match. This combines what would normally be two separate steps, parsing and validation, into a single fast operation. Encoding goes the other way: a Python Struct gets serialized into bytes in whichever format you choose. The library can also be used purely for its fast JSON or MessagePack encoding and decoding without any schema validation, for cases where you just need raw speed. A Struct behaves similarly to a dataclass or an attrs class, so developers already familiar with those patterns will find the API straightforward. The README notes that common operations on Structs are five to sixty times faster than the equivalent dataclass operations in benchmarks. The library has no required dependencies and is available on PyPI and conda-forge. It is released under the New BSD license. The project's documentation site covers the full API, extension points for adding support for custom types, and detailed benchmarks comparing it to other Python serialization libraries.