simplejson is a simple, fast, complete, correct and extensible JSON <http://json.org> encoder and decoder for Python 3.9+ with legacy support for Python 2.7. It is pure Python code with no dependencies, but includes an optional C extension for a serious speed boost.

The latest documentation for simplejson can be read online here: https://simplejson.readthedocs.io/

simplejson is the externally maintained development version of the json library included with Python (since 2.6). This version is tested with Python 3.14 (including free-threaded builds) and maintains backwards compatibility with Python 3.9+. A legacy Python 2.7 wheel is also published.

The encoder can be specialized to provide serialization in any kind of situation, without any special support by the objects to be serialized (somewhat like pickle). This is best done with the default kwarg to dumps.

The decoder can handle incoming JSON strings of any specified encoding (UTF-8 by default). It can also be specialized to post-process JSON objects with the object_hook or object_pairs_hook kwargs. This is particularly useful for implementing protocols such as JSON-RPC that have a richer type system than JSON itself.

For those of you that have legacy systems to maintain, there is a very old fork of simplejson in the python2.2 branch that supports Python 2.2. This is based on a very old version of simplejson, is not maintained, and should only be used as a last resort.

RawJSON allows embedding pre-encoded JSON strings into output without re-encoding them.

This can be useful in advanced cases where JSON content is already serialized and re-encoding would be unnecessary.

Example usage:

from simplejson import dumps, RawJSON

payload = {
    "status": "ok",
    "data": RawJSON('{"a": 1, "b": 2}')
}

print(dumps(payload))
# Output: {"status": "ok", "data": {"a": 1, "b": 2}}

Caveat: RawJSON should be used with care. It bypasses normal serialization and validation, and is not recommended for general use unless the embedded JSON content is fully trusted.