msgpack

MessagePack has been solid in production for binary serialization needs where JSON is too verbose. The C extension makes it genuinely fast, and the API is dead simple—packb() and unpackb() do what you expect. The strict/raw mode options give you control over string handling, which matters when dealing with mixed binary/text data.

From a security perspective, there are important considerations. By default, unpackb() has max_buffer_size limits which is good, but you need to explicitly set strict_map_key=False if deserializing untrusted data with non-string keys (otherwise you get confusing errors). The library doesn't prevent deserialization attacks inherent to any serialization format—you're still responsible for validating data types and ranges after unpacking. No automatic schema validation exists, so input validation is entirely on you.

Error messages are terse but not dangerously verbose—exceptions don't leak internal state. The library hasn't had major CVEs, and the maintainers are responsive to security reports. My main gripe is the documentation assumes you know MessagePack's type system already; the Python-specific gotchas around extension types and timestamp handling aren't well explained.

MessagePack provides exceptionally fast binary serialization that's more compact than JSON and cross-language compatible. The C extension makes it significantly faster than pure Python alternatives. The API is straightforward - packb() and unpackb() mirror pickle's interface, making adoption easy. I've used it extensively for IPC and cache serialization where performance matters.

The critical security concern is deserialization safety. By default, msgpack can deserialize arbitrary object types which opens code execution risks when handling untrusted data. You must explicitly set strict_map_key=False or use raw=True and handle type checking yourself. The library doesn't fail securely by default - it's on you to configure it properly. Error messages on malformed input can be cryptic, making debugging frustrating.

Type handling requires attention: Python's None, booleans, integers, floats, strings, bytes, lists, and dicts work well, but datetime objects need custom ext_hook handlers. The max_buffer_size parameter is essential for DoS prevention but isn't enforced by default. Overall solid for trusted internal systems but requires careful configuration for any untrusted input scenarios.

After using msgpack extensively in high-throughput microservices and caching layers, it's become my go-to for binary serialization. The C extension provides exceptional performance - easily 5-10x faster than JSON with 30-40% smaller payloads. Memory usage is predictable and minimal, with no surprises under load. The packb/unpackb API is dead simple, and the Packer/Unpacker classes give you fine-grained control over streaming and buffer management when you need it.

The library handles edge cases gracefully. You get sensible defaults for strict_map_key and raw/unicode handling, though you'll want to explicitly configure these for production. Type mapping between Python and MessagePack is well-documented, and the use_bin_type flag helps bridge compatibility between msgpack versions. Error messages are clear when you hit type limitations.

Resource management is solid - no connection pooling needed since it's just serialization, but the streaming Unpacker is crucial for handling large payloads without loading everything into memory. I've run this under heavy load (10K+ req/sec) with zero issues. The API has been stable for years, making upgrades painless.