---
title: "JSON to Rust Serde Struct Generator | JSON Lark"
description: "Generate Rust structs for serde from JSON samples: rename attributes, Option<T>, untagged enums for mixed values and derive options. In your browser."
url: https://jsonlark.me/json-to-rust/
---

Sheet 04 Serde structs

# JSON to Rust

Paste JSON samples and get Rust structs that derive Serialize and Deserialize, with snake_case fields mapped back to your keys.

## How it works

Fields are snake_case. For each struct the generator picks the `rename_all` rule that matches the most keys (`camelCase`, `kebab-case` and so on) and adds `#[serde(rename = "...")]` only where a key still differs. Keywords become raw identifiers such as `r#type`.

- **Option<T>**: Keys missing from some objects and values that can be null become `Option`. With "Skip None", keys that were missing are left out again when serializing, so the output matches the input.
- **Mixed values**: A value that is sometimes a number and sometimes a string becomes an `#[serde(untagged)]` enum with one variant per kind. Values of unknown type are `serde_json::Value`.
- **Derives**: `Serialize` and `Deserialize` are always derived. With `Default`, untagged enums get a small `impl Default`, since an enum with data cannot derive it.

## Questions

**Which crates does the code need?**

serde with the derive feature and serde_json: add serde = { version = "1", features = ["derive"] } and serde_json = "1" to Cargo.toml, then parse with serde_json::from_str::<Root>(text).

**Why i64 and f64?**

JSON numbers have no size, so integers become i64 (u64 when larger positive values appear) and anything with a fraction or exponent becomes f64.

**Is my JSON uploaded?**

No. The code is generated by JavaScript running in this tab, and nothing you paste leaves it. The site counts page views with Cloudflare Web Analytics, which sets no cookies and never receives what you paste.