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msgspec is a fast serialization and validation library, with builtin support for JSON, MessagePack, YAML, and TOML. It features:

  • 🚀 High performance encoders/decoders for common protocols. The JSON and MessagePack implementations regularly benchmark as the fastest options for Python.

  • 🎉 Support for a wide variety of Python types. Additional types may be supported through extensions.

  • 🔍 Zero-cost schema validation using familiar Python type annotations. In benchmarks msgspec decodes and validates JSON faster than orjson can decode it alone.

  • A speedy Struct type for representing structured data. If you already use dataclasses or attrs, structs should feel familiar. However, they're 5-60x faster for common operations.

All of this is included in a lightweight library with no required dependencies.

msgspec may be used for serialization alone, as a faster JSON or MessagePack library. For the greatest benefit though, we recommend using msgspec to handle the full serialization & validation workflow:

Define your message schemas using standard Python type annotations.

>>> import msgspec

>>> class User(msgspec.Struct):
...     """A new type describing a User"""
...     name: str
...     groups: set[str] = set()
...     email: str | None = None

Encode messages as JSON, or one of the many other supported protocols.

>>> alice = User("alice", groups={"admin", "engineering"})

>>> alice
User(name='alice', groups={"admin", "engineering"}, email=None)

>>> msg = msgspec.json.encode(alice)

>>> msg

Decode messages back into Python objects, with optional schema validation.

>>> msgspec.json.decode(msg, type=User)
User(name='alice', groups={"admin", "engineering"}, email=None)

>>> msgspec.json.decode(b'{"name":"bob","groups":[123]}', type=User)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
msgspec.ValidationError: Expected `str`, got `int` - at `$.groups[0]`

msgspec is designed to be as performant as possible, while retaining some of the nicities of validation libraries like pydantic. For supported types, encoding/decoding a message with msgspec can be ~10-80x faster than alternative libraries.

See the documentation for more information.


New BSD. See the License File.