UltraJSON UltraJSON is an ultra fast JSON encoder and decoder written in pure C with bindings for Python 3.8+. Install with pip: python -m pip install ujson Project status Warning UltraJSON's architecture is fundamentally ill-suited to making changes without risk of introducing new security vulnerabilities. As a result, this library has been put into a maintenance-only mode. Support for new Python versions will be added and critical bugs and security issues will still be fixed but all other changes will be rejected. Users are encouraged to migrate to orjson which is both much faster and less likely to introduce a surprise buffer overflow vulnerability in the future. Usage May be used as a drop in replacement for most other JSON parsers for Python: >>> import ujson >>> ujson.dumps([{ " key " : " value " }, 81 , True ]) '[{"key":"value"},81,true]' >>> ujson.loads( """ [{"key": "value"}, 81, true] """ ) [{'key': 'value'}, 81, True] Encoder options encode_html_chars Used to enable special encoding of "unsafe" HTML characters into safer Unicode sequences. Default is False : >>> ujson.dumps( " <script>John&Doe " , encode_html_chars = True ) '"\\u003cscript\\u003eJohn\\u0026Doe"' ensure_ascii Limits output to ASCII and escapes all extended characters above 127. Default is True . If your end format supports UTF-8, setting this option to false is highly recommended to save space: >>> ujson.dumps( " aao " ) '"\\u00e5\\u00e4\\u00f6"' >>> ujson.dumps( " aao " , ensure_ascii = False ) '"aao"' escape_forward_slashes Controls whether forward slashes ( / ) are escaped. Default is True : >>> ujson.dumps( " https://example.com " ) '"https:\\/\\/example.com"' >>> ujson.dumps( " https://example.com " , escape_forward_slashes = False ) '"https://example.com"' indent Controls whether indentation ("pretty output") is enabled. Default is 0 (disabled): >>> ujson.dumps({ " foo " : " bar " }) '{"foo":"bar"}' >>> print (ujson.dumps({ " foo " : " bar " }, indent = 4 )) { "foo":"bar" } Benchmarks UltraJSON calls/sec compared to other popular JSON parsers with performance gain specified below each. Test machine Linux 5.15.0-1037-azure x86_64 #44-Ubuntu SMP Thu Apr 20 13:19:31 UTC 2023 Versions CPython 3.11.3 (main, Apr 6 2023, 07:55:46) [GCC 11.3.0] ujson : 5.7.1.dev26 orjson : 3.9.0 simplejson : 3.19.1 json : 2.0.9 ujson orjson simplejson json Array with 256 doubles encode 18,282 79,569 5,681 5,935 decode 28,765 93,283 13,844 13,367 Array with 256 UTF-8 strings encode 3,457 26,437 3,630 3,653 decode 3,576 4,236 522 1,978 Array with 256 strings encode 44,769 125,920 21,401 23,565 decode 28,518 75,043 41,496 42,221 Medium complex object encode 11,672 47,659 3,913 5,729 decode 12,522 23,599 8,007 9,720 Array with 256 True values encode 110,444 425,919 81,428 84,347 decode 203,430 318,193 146,867 156,249 Array with 256 dict{string, int} pairs encode 14,170 72,514 3,050 7,079 decode 19,116 27,542 9,374 13,713 Dict with 256 arrays with 256 dict{string, int} pairs encode 55 282 11 26 decode 48 53 27 34 Dict with 256 arrays with 256 dict{string, int} pairs, outputting sorted keys encode 42 8 27 Complex object encode 462 397 444 decode 480 618 177 310 Above metrics are in call/sec, larger is better. Build options For those with particular needs, such as Linux distribution packagers, several build options are provided in the form of environment variables. Debugging symbols UJSON_BUILD_NO_STRIP By default, debugging symbols are stripped on Linux platforms. Setting this environment variable with a value of 1 or True disables this behavior. Using an external or system copy of the double-conversion library These two environment variables are typically used together, something like: export UJSON_BUILD_DC_INCLUDES= ' /usr/include/double-conversion ' export UJSON_BUILD_DC_LIBS= ' -ldouble-conversion ' Users planning to link against an external shared library should be aware of the ABI-compatibility requirements this introduces when upgrading system libraries or copying compiled wheels to other machines. UJSON_BUILD_DC_INCLUDES One or more directories, delimited by os.pathsep (same as the PATH environment variable), in which to look for double-conversion header files; the default is to use the bundled copy. UJSON_BUILD_DC_LIBS Compiler flags needed to link the double-conversion library; the default is to use the bundled copy.