I released a new JSON encoding/decoding library that uses NIF C++ backend and consistently outperforms most of other implementations.

Fast Erlang NIF JSON encoder/decoder backed by the glaze C++ library, with a hand-rolled recursive-descent decoder and direct term-to-JSON encoder that produce/consume native Erlang terms in a single pass.

Features

• Decoding straight to Erlang terms: maps, lists, binaries, integers (including bignums), floats, booleans, and null
• Encoding Erlang terms straight to JSON, including big integers
• Configurable representation of JSON null and JSON object keys
• minify/1 and prettify/1 helpers
• Standalone big-integer encode/decode helpers (encode_bigint/1, decode_bigint/1)

(numbers in µs)
JSON files:   twitter (616.7K)     twitter2 (758.0K)     openrtb (1.2K)      esad (1.3K)         small (0.1K)
               decode   encode     decode   encode     decode   encode     decode   encode     decode   encode
---------------------------------------------------------------------------------------------------------------------
glazejson     10097.9   3947.9    14904.2   8186.0       17.4     12.5       14.8      8.7        1.3      1.5
torque        10151.7   4358.7    12899.5   6798.9       18.3     13.2       19.9      7.1        4.5      1.7
simdjsone     10345.9   7541.2    18973.3  13482.5       25.6     27.5       19.5     18.5        1.7      4.5
jiffy         30645.2   4347.6    51053.1   9500.1       50.0     28.6       32.2     19.0        7.4      4.2
jason         21005.7  12918.1    40277.2  25064.8       56.4     26.2       33.7     22.1        6.0      3.7
thoas         21151.4  13779.6    41390.0  25625.0       57.4     29.9       35.0     26.7        7.5      3.8
euneus        20488.9  12319.9    31853.9  25111.0       40.7     32.7       25.2     19.0        7.3      3.3
json          19887.1  11679.8    30902.8  24087.7       41.5     26.9       40.1     10.6        4.8      4.1