msgpack
MessagePack binary serialization library for Python — faster and more compact than JSON for serializing Python objects. msgpack features: msgpack.packb() for serialization to bytes, msgpack.unpackb() for deserialization, Unpacker for streaming, use_bin_type=True for Python 3 str/bytes distinction, raw=False for str output, strict_map_key for security, Packer class for repeated packing, ext_type for custom types, and C extension for maximum speed. MessagePack format is 20-50% smaller than equivalent JSON.
Score Breakdown
⚙ Agent Friendliness
🔒 Security
Binary serialization library. No code execution on deserialization (unlike pickle) — safe for untrusted input. Set max_buffer_size to prevent memory exhaustion. Validate data types after unpacking. Binary format harder to inspect than JSON — use logging for debugging.
⚡ Reliability
Best When
High-throughput binary serialization for inter-process or inter-service communication where JSON overhead matters — msgpack is faster and smaller than JSON with cross-language support.
Avoid When
Human-readable output needed (use JSON), Python-only caching (use pickle or orjson), or when msgpack's binary format complicates debugging.
Use Cases
- • Agent binary serialization — import msgpack; packed = msgpack.packb({'id': 1, 'data': [1,2,3], 'name': 'test'}, use_bin_type=True); unpacked = msgpack.unpackb(packed, raw=False) — binary pack/unpack; agent uses msgpack for inter-process communication or cache storage where binary is acceptable
- • Agent Redis cache with msgpack — r = redis.Redis(); data = {'key': 'value', 'numbers': [1, 2, 3]}; r.set('cache:key', msgpack.packb(data, use_bin_type=True)); cached = msgpack.unpackb(r.get('cache:key'), raw=False) — compact cache; agent stores compact binary data in Redis; smaller than JSON for same data
- • Agent Celery serialization — app.conf.task_serializer = 'msgpack'; app.conf.result_serializer = 'msgpack'; app.conf.accept_content = ['msgpack'] — celery integration; agent configures Celery to use msgpack for task serialization; requires kombu[msgpack] extra
- • Agent streaming unpack — from msgpack import Unpacker; unpacker = Unpacker(raw=False); for chunk in data_stream: unpacker.feed(chunk); for unpacked in unpacker: process(unpacked) — streaming; agent processes continuous stream of msgpack messages (WebSocket, network stream)
- • Agent custom types — def default(obj): if isinstance(obj, datetime): return msgpack.ExtType(1, obj.isoformat().encode()); raise TypeError; def ext_hook(code, data): if code == 1: return datetime.fromisoformat(data.decode()); return msgpack.ExtType(code, data); packed = msgpack.packb(obj, default=default); unpacked = msgpack.unpackb(packed, ext_hook=ext_hook, raw=False) — custom; agent serializes datetime via ExtType
Not For
- • Human-readable data — msgpack is binary; for human-readable use JSON
- • Cross-language with complex types — msgpack base types work cross-language; custom ExtType requires coordinated extension handling in each language
- • Simple Python-only caching — for Python-only caching pickle is simpler; msgpack's advantage is cross-language and security (no code execution)
Interface
Authentication
No auth — serialization library.
Pricing
msgpack-python is Apache 2.0 licensed. Free for all use.
Agent Metadata
Known Gotchas
- ⚠ use_bin_type=True and raw=False required for Python 3 — msgpack.packb(data) without use_bin_type=True encodes str as bytes in legacy mode; msgpack.unpackb(data) without raw=False returns bytes for strings; agent code: ALWAYS use: msgpack.packb(data, use_bin_type=True) and msgpack.unpackb(data, raw=False); otherwise str/bytes confusion in Python 3
- ⚠ strict_map_key=False may be needed — msgpack.unpackb(data, raw=False) by default requires map keys to be str (strict_map_key=True); int keys cause msgpack.exceptions.UnpackValueError; agent code receiving msgpack from other systems with int keys: unpackb(data, raw=False, strict_map_key=False); or use strict_map_key=True and ensure sender uses string keys
- ⚠ No datetime/UUID native support — msgpack base spec has int, float, str, bytes, list, dict; datetime and UUID must use custom ExtType or convert to str/int before packing; agent code: convert datetime.isoformat() before packing; use default= function for custom types; or use ext_type for cross-language datetime
- ⚠ Streaming Unpacker requires feed() — Unpacker() does not accept bytes at construction; unpacker.feed(chunk) then iterate: for obj in unpacker: process(obj); agent code reading from socket: while True: chunk = sock.recv(4096); unpacker.feed(chunk); for obj in unpacker: handle(obj) — correct streaming pattern
- ⚠ Integer size affects encoding size — msgpack uses variable-length encoding; small integers (0-127) use 1 byte; large integers use more; Python large int beyond int64: msgpack raises OverflowError; agent code: ensure integers fit int64 range; for large numbers use str representation
- ⚠ max_buffer_size for streaming — Unpacker(max_buffer_size=N) limits memory buffer; default 100MB; large messages may exceed; agent code processing large msgpack messages: increase max_buffer_size or use packb/unpackb for complete messages instead of streaming
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Scores are editorial opinions as of 2026-03-06.