JSON Processing in Rust: serde_json and Alternatives |…

JSON Processing in Rust: Overview of Key Libraries and Tools

JSON (JavaScript Object Notation) remains one of the most popular formats for data exchange between services, configuration files, and APIs. In the Rust ecosystem, there are several powerful libraries for working with JSON, each solving its own tasks — from maximum performance to ease of development. In this article, we will thoroughly examine the main tools: serde_json, simd-json, json5, jsonwebtoken and show how to use them in real projects.

1. serde_json — The De Facto Standard

serde_json is the primary library for JSON serialization and deserialization in Rust. It is built on top of the serde framework, which allows automatic conversion of Rust data structures to and from JSON.

Installation: add to Cargo.toml:

[dependencies]serde = { version = "1.0", features = ["derive"] }serde_json = "1.0"

Example: Serialization and Deserialization

use serde::{Deserialize, Serialize};use serde_json::Result;

#[derive(Serialize, Deserialize, Debug)]struct User {    name: String,    age: u8,    email: Option<String>,}

fn main() -> Result<()> {    let user = User {        name: "Anna".to_string(),        age: 30,        email: Some("anna@example.com".to_string()),    };

    // Serialize to JSON string    let json_string = serde_json::to_string(&user)?;    println!("JSON: {}", json_string);

    // Deserialize back to struct    let deserialized: User = serde_json::from_str(&json_string)?;    println!("{:?}", deserialized);

    Ok(())}

Features:

Support for nested structures, enums, and optional fields.
Working with arbitrary JSON via serde_json::Value (enum with variants Null, Bool, Number, String, Array, Object).
Custom serializers through attributes #[serde(rename)], #[serde(skip)] and others.
Streaming processing for large files.

When to use: for 95% of projects — this is the best choice. It is stable, well-documented, and integrates with any web frameworks (Actix, Rocket, Axum).

2. simd-json — Maximum Performance

simd-json is a library that uses CPU SIMD instructions (Single Instruction, Multiple Data) to accelerate JSON parsing. According to benchmarks, it is 2–3 times faster than serde_json on large data volumes.

Installation:

[dependencies]simd-json = "0.14"

Example: Fast Parsing

use simd_json::prelude::*;use simd_json::BorrowedValue;

fn main() {    let mut data = br#"[{"city":"Moscow","temp":22},{"city":"SPb","temp":18}]"#.to_vec();    // Parsing with mutation of input data (for speed)    let value: BorrowedValue = simd_json::to_borrowed_value(&mut data).unwrap();        if let Some(arr) = value.as_array() {        for item in arr {            let city = item.get("city").and_then(|v| v.as_str()).unwrap_or("unknown");            let temp = item.get("temp").and_then(|v| v.as_f64()).unwrap_or(0.0);            println!("{}: {}°C", city, temp);        }    }}

Features: