valyala/fastjson

Health v2 · maintenance only

Flags: no_releases

Adoption not part of the score

2466 stars · 157 forks observed · 2026-08-28

What it is AI-extracted, prompt v1, taxonomy v1, 2026-08-30, confidence not recorded

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

library · maturity stable

serialization parser developer-tools backend performance go cross-platform -parser -validation zero-allocation no-reflection high-performance

Member repositories

For agents

markdown · JSON · MCP: product_card(name="valyala/fastjson")