Zero-copy JSON for Rust. A proc-macro generates a typed, monomorphised parser and serializer per struct at compile time — no runtime dispatch, no intermediate Value, no unnecessary allocations.

Add jzon-rs. The derive feature is on by default.

[dependencies]
jzon-rs = "0.2"

use jzon::{ToJson, FromJson};

#[derive(ToJson, FromJson)]
#[serde(rename_all = "camelCase")]
struct User<'a> {
    id:    u64,
    name:  &'a str,  // zero-copy: borrows directly from the input bytes
    score: f64,
}

let user = User::from_json_str(input)?;
let out  = user.to_json_string();

Add jzon-rs-serde. No other changes to your code.

[dependencies]
jzon-rs-serde = "0.2"
serde = { version = "1", features = ["derive"] }

use serde::{Serialize, Deserialize};

#[derive(Serialize, Deserialize)]
struct User<'a> { id: u64, name: &'a str }

let user: User = jzon_serde::from_str(input)?;
let out = jzon_serde::to_string(&user)?;

Add one line to your workspace Cargo.toml. Zero code changes required — every serde_json call across your entire dep tree (reqwest, axum, etc.) routes through jzon automatically.

[patch.crates-io]
serde_json = { package = "jzon-rs-compat", version = "0.2" }

Both crates expose the same flags: simd, fast-float, unstable, stats. jzon-rs-compat also has fast-float on by default (sensible for a drop-in replacement).

Up to 3.6× serde_json, 2.4× sonic-rs, 7.8× simd-json on real-world workloads. Top: 55.92 GiB/s twitter serialize

Full matrix + competitor comparison + workloads where we lose: BENCHMARKS.md.

• Field dispatch as u64 compare — keys ≤ 8 bytes match in one CPU instruction. A one-word field-hint variable predicts the next key, so in-order JSON dispatches O(1) without hashing.
• Zero-copy — &'de str fields borrow directly from input bytes; no allocation unless the string has escapes.
• Hand-written SIMD — aarch64 NEON + x86_64 SSE2/AVX2 intrinsics for find_quote_or_backslash and find_escape. Up to 5.6× over u128 SWAR.
• fast_float2 for parsing, ryu or zmij for serializing.

rename, rename_all (8 modes), skip, skip_serializing, skip_deserializing, skip_serializing_if, default, alias, deny_unknown_fields, tag (internally-tagged enums), transparent.

Types: all primitives, String, &'de str, Option<T>, Vec<T>, HashMap, BTreeMap, char, (), tuples 1–12, u128/i128, newtype structs, tuple structs, enum struct variants.

Made with ❤️ by Rajaniraiyn