# valyala/fastjson

Fast JSON parser and validator for Go. No custom structs, no code generation, no reflection

Repository: https://github.com/valyala/fastjson
Canonical: https://ross.abutalabs.com/products/valyala-fastjson
Language: Go
License: MIT
License Family: permissive
Topics: json-parser, fast, golang, go, json, json-validation
Last push: 2026-02-21T12:17:08+00:00

## Health v2 (maintenance only)
Score: 63/100 (v2, computed 2026-09-03T02:20:16.233290+00:00)
- activity 68, release rhythm 35, longevity 100
- inputs: {"age_days": 3019, "days_push": 193, "days_rel": null, "gap_med": null, "n_releases_24m": 0}
- flags: no_releases
- formula: round(0.45*activity + 0.35*rhythm + 0.20*longevity); archived -> min(score, 10)

## Adoption (not part of the score)
Stars 2466, forks 157 (observed 2026-08-28T04:06:53.683626+00:00)

## What it is
fast is a fast JSON parser and validator library for Go that parses arbitrary JSON without schemas, reflection, or code generation. It claims up to 15x faster performance than the standard encoding/ package and validates JSON while parsing.

## Use cases
- parse  quickly in go without structs
- validate  payloads in a hot path
- extract a few fields from large  documents
- parse  arrays with mixed value types
- modify and re-marshal parts of a  document
- replace encoding/ for performance-critical parsing

## When to choose
- you need maximum  parsing throughput in Go
- you want schema-less parsing without code generation or reflection
- you access multiple unrelated fields and want a single parse pass
- you need  validation during parsing

## When to avoid
- you want simple struct-based marshaling like encoding/
- you need to parse  from io.Reader streams
- you prefer a garbage-collected API without manual arena/parser reuse rules
- your team cannot handle the careful memory-reuse requirements

## Facets
- artifact type: library
- maturity: stable
- function: serialization, parser
- domain: developer-tools, backend, performance
- platform: go, cross-platform
- tags: -parser, -validation, zero-allocation, no-reflection, high-performance

## Member repositories
- valyala/fastjson (main) score 63

## Provenance
- Observed fields: from GitHub, fetched 2026-08-28T04:06:53.683626+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 2026-08-30T02:29:13.911553+00:00, confidence not recorded.
  - readme: https://github.com/valyala/fastjson (fetched 2026-08-28T04:06:53.683626+00:00, sha 6fbc40d799f7)
- Data as of 2026-08-30T08:39:29.467469+00:00.