simplejson
Extended JSON encoder/decoder for Python — a faster, more feature-rich drop-in replacement for the stdlib json module. simplejson features: use_decimal=True for Decimal serialization, namedtuple_as_object for namedtuple handling, tuple_as_array, item_sort_key for sorted output, for_json protocol via __for_json__ method, JSONDecodeError with location info, encoding parameter for bytes handling, allow_nan flag, raw_json() for embedding pre-serialized JSON, C extension speedup, and full json module API compatibility (loads/dumps/load/dump).
Score Breakdown
⚙ Agent Friendliness
🔒 Security
JSON serialization library with no network calls. simplejson.loads() is not vulnerable to eval injection (unlike ast.literal_eval on malformed input). Large JSON documents can cause DoS via memory exhaustion — validate document size before parsing untrusted JSON. No deserialization vulnerabilities (unlike pickle/dill).
⚡ Reliability
Best When
JSON encoding with Decimal support, custom object protocols, or sorted deterministic output — simplejson is a drop-in json replacement for edge cases the stdlib json doesn't handle.
Avoid When
Maximum performance (use orjson), binary formats (use msgpack), or schema validation (use pydantic/jsonschema).
Use Cases
- • Agent Decimal handling — import simplejson as json; from decimal import Decimal; data = {'price': Decimal('19.99'), 'tax': Decimal('1.80')}; json.dumps(data, use_decimal=True) — '{"price": 19.99, "tax": 1.80}' — Decimal serialization; agent financial data round-trips without floating point precision loss; stdlib json raises TypeError for Decimal
- • Agent sorted JSON output — import simplejson as json; json.dumps(config, sort_keys=True, indent=2) — deterministic output; agent generated JSON files are diff-friendly in version control; sorted keys ensure same dict always produces same JSON string
- • Agent custom object serialization — class AgentState: def __for_json__(self): return {'status': self.status, 'memory': self.memory}; json.dumps(state) — __for_json__ protocol; agent custom objects serialize without custom encoder class; simpler than json.JSONEncoder subclass
- • Agent JSON error location — try: simplejson.loads(bad_json); except simplejson.JSONDecodeError as e: print(f'Error at line {e.lineno}, col {e.colno}: {e.msg}') — error with location; agent parses user-provided JSON and reports error location; stdlib json also has location but simplejson's is more accurate for large documents
- • Agent raw JSON embedding — from simplejson import raw_json; data = {'metadata': raw_json(precomputed_json_string)}; simplejson.dumps(data) — embed pre-serialized JSON without re-parsing; agent embeds cached JSON blob into larger response without deserialize/re-serialize overhead
Not For
- • High-performance JSON — for maximum speed use orjson (Rust-based, 3-10x faster than simplejson)
- • Binary JSON formats — simplejson is text JSON only; for binary use MessagePack or CBOR
- • Schema validation — simplejson is encoding/decoding only; for validation use jsonschema or pydantic
Interface
Authentication
No auth — local JSON serialization library.
Pricing
simplejson is MIT licensed. Free for all use.
Agent Metadata
Known Gotchas
- ⚠ import simplejson as json not required but conventional — simplejson is API-compatible with stdlib json; most code uses: import simplejson as json; then calls json.loads()/json.dumps() identically to stdlib; some packages check type(json).__name__ == 'json' — rare issue but possible with strict type checking
- ⚠ use_decimal=True changes loads() behavior too — simplejson.loads('19.99', use_decimal=True) returns Decimal('19.99') not float; agent code using use_decimal=True for dumps must also use it for loads() if round-trip Decimal fidelity is needed; mixing use_decimal in dumps but not loads converts Decimal to float on reload
- ⚠ C extension may not be compiled — pip install simplejson on systems without C compiler falls back to pure Python; agent Docker images using Alpine Linux need build tools: apk add gcc python3-dev musl-dev; pure Python mode is slower but correct; no warning is emitted about pure Python mode
- ⚠ JSONDecodeError is simplejson.JSONDecodeError not json.JSONDecodeError — agent code catching json.JSONDecodeError may miss simplejson.JSONDecodeError; import simplejson; except simplejson.JSONDecodeError: is correct; simplejson.JSONDecodeError is a subclass of ValueError like stdlib
- ⚠ raw_json() bypasses validation — simplejson.raw_json(invalid_json_string) creates wrapper without parsing; the invalid JSON is embedded as-is in output; resulting JSON document is invalid; agent code using raw_json() must pre-validate the string or risk producing malformed JSON
- ⚠ namedtuple_as_object default is False — simplejson.dumps(Point(1, 2)) serializes namedtuple as [1, 2] by default (list); simplejson.dumps(Point(1, 2), namedtuple_as_object=True) produces {'x': 1, 'y': 2}; agent code expecting dict-style namedtuple serialization must set namedtuple_as_object=True explicitly
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Scores are editorial opinions as of 2026-03-06.