msgspec

A fast serialization and validation library, with builtin support for JSON, MessagePack, YAML, and TOML.

msgspec Permissive license BSD-3-Clause Active ★ 4,007 v0.21.1 released 2026-04-12

Install

msgspec on PyPI

pip

pip install msgspec

uv

uv add msgspec

poetry

poetry add msgspec

Package facts

License	BSD-3-Clause (permissive)
Python support	supports the current Python release (>=3.10)
Install friction	medium — platform-specific wheel
Runtime dependencies	none
Maintenance	actively maintained — 123 days since the last release
Last repo commit	2026-08-12
First released	2021-02-23
Popularity	one of the top 1,000 most-downloaded packages on PyPI (30-day window, as of 2026-08-13)
Known vulnerabilities	none known (OSV.dev, checked 2026-08-13)

Evidence: msgspec-0.21.1-cp310-cp310-macosx_10_9_x86_64.whl; msgspec-0.21.1-cp310-cp310-macosx_11_0_arm64.whl; msgspec-0.21.1-cp310-cp310-manylinux2014_aarch64.manylinux_2_17_aarch64.manylinux_2_28_aarch64.whl; msgspec-0.21.1-cp310-cp310-manylinux2014_x86_64.manylinux_2_17_x86_64.manylinux_2_28_x86_64.whl; msgspec-0.21.1-cp310-cp310-musllinux_1_2_aarch64.whl; msgspec-0.21.1-cp310-cp310-musllinux_1_2_x86_64.whl; msgspec-0.21.1-cp310-cp310-win_amd64.whl; msgspec-0.21.1-cp310-cp310-win_arm64.whl; msgspec-0.21.1-cp311-cp311-macosx_10_9_x86_64.whl; msgspec-0.21.1-cp311-cp311-macosx_11_0_arm64.whl; msgspec-0.21.1-cp311-cp311-manylinux2014_aarch64.manylinux_2_17_aarch64.manylinux_2_28_aarch64.whl; msgspec-0.21.1-cp311-cp311-manylinux2014_x86_64.manylinux_2_17_x86_64.manylinux_2_28_x86_64.whl; msgspec-0.21.1-cp311-cp311-musllinux_1_2_aarch64.whl; msgspec-0.21.1-cp311-cp311-musllinux_1_2_x86_64.whl; msgspec-0.21.1-cp311-cp311-win_amd64.whl; msgspec-0.21.1-cp311-cp311-win_arm64.whl; msgspec-0.21.1-cp312-cp312-macosx_10_13_x86_64.whl; msgspec-0.21.1-cp312-cp312-macosx_11_0_arm64.whl; msgspec-0.21.1-cp312-cp312-manylinux2014_aarch64.manylinux_2_17_aarch64.manylinux_2_28_aarch64.whl; msgspec-0.21.1-cp312-cp312-manylinux2014_x86_64.manylinux_2_17_x86_64.manylinux_2_28_x86_64.whl

Keywords: JSON, MessagePack, TOML, YAML, msgpack, schema, serialization, validation

Development Status :: 4 - BetaProgramming Language :: Python :: 3.10Programming Language :: Python :: 3.11Programming Language :: Python :: 3.12Programming Language :: Python :: 3.13Programming Language :: Python :: 3.14

About msgspec

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AI interpretation — verify before relying

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msgspec is a fast serialization and validation library supporting JSON, MessagePack, YAML, and TOML with zero-cost schema validation using Python type annotations and a high-performance Struct type for structured data.

Medium install friction due to compiled wheels for multiple Python versions and platforms (3.10–3.14, x86_64/arm64, Linux/macOS/Windows), but no runtime dependencies and active maintenance (last commit 2026-08-12) reduce practical concern.

BSD-3-Clause (permissive) allows commercial and private use with minimal restrictions; attribution and license inclusion in distributions are the primary obligations.

Usage

import msgspec

class User(msgspec.Struct):
    name: str
    email: str | None = None

alice = User("alice", email="alice@example.com")
msg = msgspec.json.encode(alice)
decoded = msgspec.json.decode(msg, type=User)

Requires Python 3.10 or later; compiled wheels are provided for common platforms but source builds require a C compiler.

Verdict: msgspec is a mature, actively maintained serialization library (4007 GitHub stars, top 1000 PyPI tier) with no known vulnerabilities, permissive licensing, and zero runtime dependencies. Medium install friction is offset by comprehensive pre-built wheels and strong performance benchmarks. Suitable for production use where fast JSON/MessagePack handling and schema validation are priorities.

Needs verification

Whether the compiled wheel for your specific platform (Python version + OS + architecture) is available in the distribution.
Performance gains relative to your current serialization approach in your specific workload.
Compatibility of msgspec's Struct type with existing dataclass or attrs codebases if migration is planned.

fast JSON serializationMessagePack encoder decoderschema validation with type hintsYAML TOML serializationhigh performance data validationstructured data serializationmsgpack python library