Is it rapid?

You bet! rapidyaml is hands down the fastest YAML processor, and among the fastest JSON processors. But talk is cheap, so this page shows performance results to substantiate this bold claim.

Linux, gcc 16

This section shows results using gcc 16.1. First, here are some performance plots with an example yaml file using parse and emit benchmarks, comparing ryml with yamlcpp, libyaml and fyaml (click the image to see the data, and see the terminology section at the end for info on the different variants):

ParseEmit

To prove that this is not coincidence for a particular file, here are scatter plots across YAML files with different styles and sizes, where we pick one of the variants above. The ryml variants are ryml_yaml_inplace_reuse_reserve and ryml_yaml_str_reserve from the plots above (again, click the image to see the data):

`
ParseEmit

In absolute terms, ryml parses at ~200MB/s and emits at ~600MB/s, and is generally 30x (parse) / 150x (emit) faster than yamlcpp, and never less than 10x (parse) / 50x (emit). These are stark numbers, and justify the library name.

Windows, Visual Studio 2026

Same plots as above (click the image to see the data):

ParseEmit
`
ParseEmit

JSON performance

ryml is also among the fastest JSON handlers. It may not be the fastest, but is well ahead of the pack; here are some performance results. The benchmark code is the same as above, and it is reading a compile_commands.json file. The json libraries are rapidjson, sajson, jsoncpp and nlohmann:

Parse performanceEmit performance

parse

MB/s

MB/s(x)

ryml_json

908.00

40.31x

ryml_yaml

881.58

39.13x

libyaml_arena

135.06

6.00x

libfyaml_arena

149.15

6.62x

yamlcpp_arena

22.53

1.00x

rapidjson_arena

756.93

33.60x

rapidjson_inplace

1741.62

77.31x

sajson_arena

592.57

26.30x

sajson_inplace

599.41

26.61x

jsoncpp_arena

298.60

13.25x

nlohmann_arena

197.17

8.75x

emit

MB/s

MB/s(x)

ryml_yaml_str

805.03

128.36x

ryml_json_str

1034.93

165.01x

fyaml_str

425.42

67.83x

yamlcpp

6.27

1.00x

rapidjson

751.47

119.82x

jsoncpp

562.65

89.71x

nlohmann

299.40

47.74x

So ryml beats most json parsers at their own game, with the only exception of rapidjson out of the tested libraries. (There are probably other JSON parsers faster than rapidyaml, likely simdjson). As for emitting, rapidyaml is hands-down the fastest, exceeding all JSON libraries tested. Even parsing full YAML is at ~200MB/s, which is still in the JSON performance ballpark, albeit at its lower end. This is something to be proud of, as the YAML specification is much more complex than JSON: 23449 vs 1969 words.

Serialization performance

Serialization speed also matters for overall speed. For (de)serialization ryml uses the charconv facilities from c4core; these functions are blazing fast, and generally outperform the fastest equivalent facilities in the standard library by a significant margin. For example, here are some results for c4::xtoa<int64_t>():

gcc 12.1Visual Studio 2019

Terminology

rapidyaml offers different ways to parse yaml; here’s a legend of the terms used above:

  • _inplace means the source is directly parsed (parse_in_place() or parse_json_in_place())

  • _arena means the source is first copied to the tree arena and then the copy is parsed (parse_in_arena() or parse_json_in_arena())

  • _reserve means the target tree or buffer was reserved to a suitable size before parsing / emitting

  • for parsing:

    • ryml_yaml means the standard ryml tree parser in YAML mode, ie by calling parse_in_arena() or parse_in_place()

    • ryml_json means the standard ryml tree parser in JSON mode, ie by calling parse_json_in_arena() or parse_json_in_place()

    • ryml_ints means the integer events parser

    • _reuse means the parser or emitter are reused during each benchmark; otherwise they are newly created and destroyed on each benchmark iteration

    • _nofilter means scalar filtering was disabled during parsing (see ParseOptions)

  • for emitting:

    • ryml_yaml means the standard ryml tree emitter in YAML mode, ie by calling emit_yaml() or emitrs_yaml()

    • ryml_json means the standard ryml tree emitter in YAML mode, ie by calling emit_yaml() or emitrs_json()

    • _str means emit to string

    • _file means emit to FILE*

    • _str_file means emit first to string, then to FILE* (40% faster than _file because it results in less system calls)

    • _ostream means emit to std::stringstream

    • _ofstream means emit to std::ofstream