# FASTJSON

🚄 FASTJSON2 is a Java JSON  library with excellent performance.

Repository: https://github.com/alibaba/fastjson2
Canonical: https://ross.abutalabs.com/products/fastjson
Language: Java
License: Apache-2.0
License Family: permissive
Topics: json, fastjson, json-parser, jsonb, java-json, json-serialization, json-path, high-performance, fastjson2, android, deserialization, json-serializer, serialization, big-data, java, json-deserialization, graal, graalvm-native-image
Last push: 2026-08-24T08:35:20+00:00
Link (homepage): https://github.com/alibaba/fastjson2/wiki/fastjson_1_upgrade_cn

## Health v2 (maintenance only)
Score: 94/100 (v2, computed 2026-09-02T17:46:02.011165+00:00)
- activity 99, release rhythm 84, longevity 100
- inputs: {"age_days": 1599, "days_push": 9, "days_rel": 31, "gap_med": 53, "n_releases_24m": 10}
- flags: none
- formula: round(0.45*activity + 0.35*rhythm + 0.20*longevity); archived -> min(score, 10)

## Adoption (not part of the score)
Stars 4397, forks 603 (observed 2026-08-28T04:08:48.212196+00:00)

## What it is
Fast is a high-performance Java JSON library for converting Java objects to JSON and back, working with arbitrary Java objects including pre-existing unmodifiable classes. Fast 2.0 is the actively maintained successor with better performance, security (autoType whitelist removed), GraalVM and Kotlin support.

## Use cases
- serialize java objects to
- parse  strings into java objects
- fast  parsing on android
- convert  to pojo without source code
- serialization for rpc payloads
- handle deeply nested generic  structures

## When to choose
- you need maximum JSON throughput on the JVM or Android
- you must serialize pre-existing classes you cannot modify
- you want a mature, widely used Java JSON library
- you need fast 1.x compatibility via fast2 compat mode

## When to avoid
- you prefer a standards-based API like Jackson or Jakarta JSON Binding
- you need cross-language JSON support beyond the JVM
- you are starting a new project and want the most mainstream ecosystem choice

## Facets
- artifact type: library
- maturity: stable
- function: serialization, parser
- domain: developer-tools, backend, apis
- platform: jvm
- tags: -parser, -serialization, deserialization, high-performance, alibaba, android

## Member repositories
- alibaba/fastjson2 (main) score 94
- alibaba/fastjson (main) score 10

## Provenance
- Observed fields: from GitHub, fetched 2026-08-28T04:08:48.212196+00:00.
- Health v2: computed from the inputs above; adoption is never an input.
- Inferred fields (summary, facets, guidance): AI-extracted, prompt v1, taxonomy v1, on 2026-08-29T16:56:01.578572+00:00, confidence not recorded.
  - readme: https://github.com/alibaba/fastjson2 (fetched 2026-08-28T04:08:48.212196+00:00, sha 681101bd6034)
  - homepage: https://github.com/alibaba/fastjson2/wiki/fastjson_1_upgrade_cn (fetched 2026-08-29T07:52:41.491444+00:00, sha bdeb71ff2ea9)
- Data as of 2026-08-30T08:39:29.467469+00:00.