json_benchmark
July 13, 2026 · View on GitHub
:grey_exclamation: Benchmarks regenerated on 2026-07-13
This repository contains benchmarks for Python JSON readers & writers. What's the fastest Python JSON parser? Let's find out.
To run the tests yourself:
git clone git@github.com:TkTech/json_benchmark.git && cd json_benchmark
<setup a virtualenv using your tool of choice>
poetry install
pytest --benchmark-json benchmark.json --benchmark-histogram histograms/
To update the tables in the README.md with the new results, just run:
python generate_benchmark_summaries.py
python generate_minefield_reports.py
Candidate Libraries
The following libraries are the current candidates for benchmarking. Feel free to request or add new libraries.
| Library | Reader | Writer | Streaming | Version |
|---|---|---|---|---|
| simdjson | Yes | No | No | 7.0.3 |
| cysimdjson | Yes | No | No | 23.9 |
| yyjson | Yes | Yes | Yes | 5.0.0 |
| orjson | Yes | Yes | No | 3.11.9 |
| rapidjson | Yes | Yes | No | 1.23 |
| ujson | Yes | Yes | No | 5.13.0 |
| json | Yes | Yes | No | 3.11 |
| msgspec | Yes | Yes | No | 0.21.1 |
| ijson | Yes | No | Yes | 3.5.1 |
"Streaming" indicates a SAX-style / incremental parser that dispatches JSON tokens without building the whole document in memory. These are compared separately in the "Streaming parse of ..." benchmark groups.
Correctness
cd It doesn't matter how fast a JSON parser is if it's not going to give you the correct results. We run the JSON minefield against each library. To see the complete line-by-line results, see the <minefield_reports/> directory.
yyjson
See full minefield results for yyjson.
| count | result |
|---|---|
| 283 | 🎉 expected result |
| 0 | 🔥 parsing should have failed but succeeded |
| 0 | 🔥 parsing should have succeeded but failed |
| 6 | ➕ result undefined, parsing succeeded |
| 29 | ➖ result undefined, parsing failed |
yyjson-sax
See full minefield results for yyjson-sax.
| count | result |
|---|---|
| 283 | 🎉 expected result |
| 0 | 🔥 parsing should have failed but succeeded |
| 0 | 🔥 parsing should have succeeded but failed |
| 6 | ➕ result undefined, parsing succeeded |
| 29 | ➖ result undefined, parsing failed |
rapidjson
See full minefield results for rapidjson.
| count | result |
|---|---|
| 277 | 🎉 expected result |
| 6 | 🔥 parsing should have failed but succeeded |
| 0 | 🔥 parsing should have succeeded but failed |
| 6 | ➕ result undefined, parsing succeeded |
| 29 | ➖ result undefined, parsing failed |
orjson
See full minefield results for orjson.
| count | result |
|---|---|
| 283 | 🎉 expected result |
| 0 | 🔥 parsing should have failed but succeeded |
| 0 | 🔥 parsing should have succeeded but failed |
| 6 | ➕ result undefined, parsing succeeded |
| 29 | ➖ result undefined, parsing failed |
simdjson
See full minefield results for simdjson.
| count | result |
|---|---|
| 283 | 🎉 expected result |
| 0 | 🔥 parsing should have failed but succeeded |
| 0 | 🔥 parsing should have succeeded but failed |
| 4 | ➕ result undefined, parsing succeeded |
| 31 | ➖ result undefined, parsing failed |
ujson
See full minefield results for ujson.
| count | result |
|---|---|
| 267 | 🎉 expected result |
| 16 | 🔥 parsing should have failed but succeeded |
| 0 | 🔥 parsing should have succeeded but failed |
| 21 | ➕ result undefined, parsing succeeded |
| 14 | ➖ result undefined, parsing failed |
msgspec
See full minefield results for msgspec.
| count | result |
|---|---|
| 283 | 🎉 expected result |
| 0 | 🔥 parsing should have failed but succeeded |
| 0 | 🔥 parsing should have succeeded but failed |
| 6 | ➕ result undefined, parsing succeeded |
| 29 | ➖ result undefined, parsing failed |
ijson
See full minefield results for ijson.
| count | result |
|---|---|
| 282 | 🎉 expected result |
| 1 | 🔥 parsing should have failed but succeeded |
| 0 | 🔥 parsing should have succeeded but failed |
| 16 | ➕ result undefined, parsing succeeded |
| 19 | ➖ result undefined, parsing failed |
Performance
In these benchmarks, lower is better.
Streaming parse of data/canada.json
Sample file is 2251051 bytes.
| library | min (ms) | max (ms) | mean (ms) |
|---|---|---|---|
| yyjson | 8.6970 | 9.3007 | 8.8893 |
| ijson (yajl2_c) | 22.6858 | 23.8652 | 23.1013 |
Streaming parse of data/citm_catalog.json
Sample file is 1727204 bytes.
| library | min (ms) | max (ms) | mean (ms) |
|---|---|---|---|
| yyjson | 3.3277 | 4.8824 | 3.7323 |
| ijson (yajl2_c) | 6.3018 | 8.5975 | 6.9487 |
Streaming parse of data/twitter.json
Sample file is 631514 bytes.
| library | min (ms) | max (ms) | mean (ms) |
|---|---|---|---|
| yyjson | 1.7940 | 2.0859 | 1.8278 |
| ijson (yajl2_c) | 2.8267 | 5.3436 | 2.9626 |
Streaming parse of data/verysmall.json
Sample file is 7 bytes.
| library | min (ms) | max (ms) | mean (ms) |
|---|---|---|---|
| yyjson | 0.0011 | 0.0212 | 0.0012 |
| ijson (yajl2_c) | 0.0037 | 0.1267 | 0.0039 |
Streaming parse of data/fgo.json
Sample file is 48765043 bytes.
| library | min (ms) | max (ms) | mean (ms) |
|---|---|---|---|
| yyjson | 315.4146 | 319.3040 | 317.5809 |
| ijson (yajl2_c) | 495.1035 | 505.1622 | 499.9637 |
Streaming parse of data/otfcc.json
Sample file is 66409302 bytes.
| library | min (ms) | max (ms) | mean (ms) |
|---|---|---|---|
| yyjson | 646.0111 | 659.2554 | 651.9847 |
| ijson (yajl2_c) | 1020.1002 | 1032.1442 | 1027.0863 |
Streaming parse of data/poet.json
Sample file is 3512883 bytes.
| library | min (ms) | max (ms) | mean (ms) |
|---|---|---|---|
| yyjson | 7.6482 | 11.5492 | 7.8543 |
| ijson (yajl2_c) | 9.3670 | 9.6594 | 9.5128 |
Streaming parse of data/gsoc-2018.json
Sample file is 3327831 bytes.
| library | min (ms) | max (ms) | mean (ms) |
|---|---|---|---|
| yyjson | 4.7380 | 5.4931 | 4.8932 |
| ijson (yajl2_c) | 5.1025 | 5.9048 | 5.2717 |
Complete load of data/canada.json
Sample file is 2251051 bytes.
| library | min (ms) | max (ms) | mean (ms) |
|---|---|---|---|
| yyjson | 4.4991 | 6.7486 | 4.8984 |
| orjson | 6.0146 | 20.8946 | 12.1758 |
| msgspec | 6.6082 | 27.9779 | 15.5113 |
| simdjson | 7.2701 | 20.6712 | 14.5211 |
| ujson | 11.1293 | 25.2489 | 18.3757 |
| json | 23.8417 | 34.6569 | 28.9730 |
| rapidjson | 24.6718 | 39.5648 | 32.8370 |
Complete load of data/citm_catalog.json
Sample file is 1727030 bytes.
| library | min (ms) | max (ms) | mean (ms) |
|---|---|---|---|
| yyjson | 1.7838 | 3.2357 | 1.9707 |
| orjson | 2.4194 | 13.5199 | 4.6141 |
| msgspec | 3.0889 | 21.4627 | 6.3947 |
| simdjson | 3.3927 | 16.4161 | 6.1467 |
| ujson | 4.4742 | 19.0578 | 7.3929 |
| rapidjson | 4.5165 | 21.7992 | 7.4734 |
| json | 6.2320 | 14.9818 | 7.9924 |
Complete load of data/twitter.json
Sample file is 567916 bytes.
| library | min (ms) | max (ms) | mean (ms) |
|---|---|---|---|
| orjson | 0.8095 | 13.5349 | 1.1043 |
| yyjson | 0.8694 | 1.5064 | 0.9441 |
| msgspec | 1.0577 | 17.2088 | 1.4776 |
| simdjson | 1.3933 | 14.9575 | 1.7529 |
| ujson | 1.6982 | 14.8908 | 2.1086 |
| rapidjson | 1.8627 | 15.8346 | 2.2719 |
| json | 2.6851 | 13.7934 | 2.9656 |
Complete load of data/verysmall.json
Sample file is 7 bytes.
| library | min (ms) | max (ms) | mean (ms) |
|---|---|---|---|
| msgspec | 0.0001 | 0.0039 | 0.0001 |
| yyjson | 0.0001 | 0.0025 | 0.0001 |
| orjson | 0.0001 | 0.0017 | 0.0001 |
| rapidjson | 0.0003 | 0.0017 | 0.0003 |
| ujson | 0.0003 | 0.0043 | 0.0003 |
| simdjson | 0.0004 | 0.0098 | 0.0004 |
| json | 0.0008 | 0.0049 | 0.0008 |
Complete load of data/fgo.json
Sample file is 45690911 bytes.
| library | min (ms) | max (ms) | mean (ms) |
|---|---|---|---|
| yyjson | 226.2088 | 239.0445 | 230.9776 |
| orjson | 470.7608 | 544.2078 | 507.9765 |
| msgspec | 474.9090 | 539.3030 | 508.0502 |
| rapidjson | 607.6599 | 671.6313 | 642.6487 |
| json | 658.0721 | 700.5949 | 674.1365 |
| ujson | 795.8875 | 926.3975 | 873.1998 |
| simdjson | 852.5420 | 919.4318 | 881.5412 |
Complete load of data/otfcc.json
Sample file is 66409251 bytes.
| library | min (ms) | max (ms) | mean (ms) |
|---|---|---|---|
| yyjson | 559.2589 | 575.5079 | 570.1669 |
| msgspec | 1051.5780 | 1180.5235 | 1115.4705 |
| orjson | 1105.1228 | 1175.1532 | 1142.0121 |
| ujson | 1286.0061 | 1469.6067 | 1364.5810 |
| rapidjson | 1296.9691 | 1427.1810 | 1359.3918 |
| simdjson | 1357.0520 | 1529.2694 | 1430.5631 |
| json | 1572.2035 | 1680.6050 | 1615.5561 |
Complete load of data/poet.json
Sample file is 1707203 bytes.
| library | min (ms) | max (ms) | mean (ms) |
|---|---|---|---|
| orjson | 4.4288 | 5.2035 | 4.5914 |
| yyjson | 4.6131 | 5.3194 | 4.7907 |
| msgspec | 4.7112 | 6.7624 | 5.3332 |
| simdjson | 5.2242 | 6.5857 | 5.4582 |
| ujson | 5.7027 | 8.0437 | 6.4811 |
| json | 6.3685 | 9.7802 | 7.2586 |
| rapidjson | 7.4218 | 8.2376 | 7.6006 |
Complete load of data/gsoc-2018.json
Sample file is 3327831 bytes.
| library | min (ms) | max (ms) | mean (ms) |
|---|---|---|---|
| msgspec | 2.5023 | 14.6973 | 3.0122 |
| yyjson | 2.5452 | 3.1216 | 2.6679 |
| simdjson | 2.8363 | 17.3013 | 3.2583 |
| orjson | 3.5744 | 14.2182 | 3.7913 |
| rapidjson | 4.3007 | 17.6994 | 4.7676 |
| json | 4.4708 | 16.9558 | 5.2436 |
| ujson | 4.6627 | 22.6703 | 5.6661 |
Merge Patch
| library | min (ms) | max (ms) | mean (ms) |
|---|---|---|---|
| json_merge_patch | 0.0005 | 0.0803 | 0.0007 |
| yyjson | 0.0010 | 0.0277 | 0.0011 |
FAQ
Why doesn't this run benchmarks using Github Actions?
Generally, unless you control the CI runners with self-hosted boxes (which are unsafe on public Github projects!), you have no idea what machine you're going to get, or how many other jobs may be running on the same machine. This can cause the benchmarks to vary drastically between runs, even minutes apart. For this reason benchmarks are always run locally on a consistent machine, in a consistent state.
What machine is used for the x64 benchmarks?
x64 tests are run on an AMD Ryzen 7 5800X, capped at base clock speed with 64GB of Corsair CMW32GX4M2E3200C16.
JSON is terrible, use X!
This repository isn't for arguing the pros or cons of JSON versus some other exchange format. You frequently have no choice but to work with JSON, and if you can read or write responses 15% faster, that means you can handle more requests per second with the same hardware.