jsonrepair-rs

Repair broken JSON in Rust.

jsonrepair-rs takes malformed JSON-like text (often from LLM output) and returns valid JSON text.

Installation

Add this to your Cargo.toml:

[dependencies]
jsonrepair-rs = "0.1"

Quick Start

This crate is a library crate (no built-in CLI binary).

use jsonrepair_rs::jsonrepair;

fn main() -> Result<(), Box<dyn std::error::Error>> {
    let broken = r#"{name: 'Alice', active: True, skills: ['Rust',],}"#;
    let repaired = jsonrepair(broken)?;

    // repaired is always a valid JSON string when Ok(...)
    println!("{repaired}");
    Ok(())
}

Output:

{"name": "Alice", "active": true, "skills": ["Rust"]}

Examples

This repository includes runnable examples in examples/:

cargo run --example repair_basic
cargo run --example repair_and_parse

repair_basic: repairs a malformed JSON-like string and prints the result.
repair_and_parse: repairs input, parses with serde_json, and validates key fields.

API

pub fn jsonrepair(input: &str) -> Result<String, JsonRepairError>

Input: malformed JSON-like text.
Output: repaired JSON string.
On failure: returns JsonRepairError with kind, position, line, and column.

If you need a typed value, parse the repaired string with serde_json:

use jsonrepair_rs::jsonrepair;

let repaired = jsonrepair("{a:1, b:2,}").unwrap();
let value: serde_json::Value = serde_json::from_str(&repaired).unwrap();
assert_eq!(value["a"], 1);

Common Repairs

Category	Examples
Quote repair	single quotes, curly quotes, backticks, unquoted keys
Comma repair	missing commas, trailing commas, leading commas
Comments	`//`, `/* */`, `#` comments are removed
Python keywords	`True` → `true`, `False` → `false`, `None` → `null`
JS keywords	`undefined`/`NaN`/`Infinity` → `null`
Markdown fences	extracts content from fenced blocks like `json ...`
Truncated JSON	auto-closes missing `]`, `}`, and string terminators
Number fixes	leading zeros, trailing dots (`2.` → `2.0`), truncated exponents
String fixes	concatenation (`"a" + "b"`), invalid escapes, control chars
JSONP	`callback({...})` → `{...}`
MongoDB wrappers	`ObjectId("...")`, `NumberLong("...")`
NDJSON	newline-delimited JSON converted to a JSON array
Ellipsis	`[1, 2, ...]` → `[1, 2]`

Error Handling

use jsonrepair_rs::{jsonrepair, JsonRepairErrorKind};

match jsonrepair("not repairable at all") {
    Ok(json) => println!("Repaired: {json}"),
    Err(e) => {
        eprintln!("kind={:?}, at {}:{} (pos={}): {}", e.kind, e.line, e.column, e.position, e.message);

        if matches!(e.kind, JsonRepairErrorKind::MaxDepthExceeded) {
            eprintln!("input nesting depth exceeded the internal limit");
        }
    }
}

Notes

Maximum supported nesting depth is 512.
When no safe repair is possible, the function returns an error instead of guessing.

Development

# Build and test
cargo build
cargo test

# CI-equivalent checks
RUSTFLAGS="-Dwarnings" cargo check --all-targets
cargo fmt --all -- --check
cargo doc --no-deps

Pre-commit

# Install pre-commit (using uv)
uv tool install pre-commit

# Install git hook for this repo
pre-commit install

# Run hooks manually
pre-commit run --all-files

Benchmarks

cargo bench

Acknowledgments

This is a Rust port of jsonrepair by Jos de Jong.

jsonrepair-rs 0.1.1