JSON to Code

Turn JSON into typed code

Paste a JSON sample, pick your target language, and get ready-to-paste type definitions — nested objects become nested types, arrays become typed lists, and field types are inferred from the values. Supports TypeScript interfaces, Go structs (with json tags), Rust structs (serde), Python dataclasses, Java classes (Jackson @JsonProperty), Kotlin data classes (kotlinx.serialization), Swift Codable structs and C# classes (System.Text.Json) — or, instead of types, a Zod schema with its z.infer type. Wherever a key has to be renamed to be a legal identifier — first_name to firstName — the original key is kept in the annotation or tag that language uses, so the code decodes the JSON it was generated from. TypeScript quotes an awkward key rather than renaming it; Python dataclasses have no such annotation, so there a renamed field is matched to its key only by the from_dict that “Add the code that reads the JSON” writes. Everything runs in your browser — your JSON is never uploaded.

The boxes under the options are all off by default, so the plain output does not change until you tick a box. Enums for strings that keep repeating turns a field that repeats a few strings into an enum in each language; Maps for objects keyed by ids reads a dictionary keyed by ids as one map type — Record<string, T>, map[string]T, Dictionary<string, T> — instead of a class per key; Types of their own for dates, UUIDs and URLs gives those strings the type each language’s decoder fills, such as time.Time, datetime or Guid; and Add the code that reads the JSON adds the function that parses it — UnmarshalRoot in Go, parse_root in Rust, a Jackson fromJson in Java, and so on. Several samples pasted one after another, JSON Lines included, are merged into one set of types, so a key only some of them have comes out optional. Some switches belong to a single language and appear only beside it: Type aliases instead of interfaces, readonly on every property and Every property optional (?) for TypeScript, omitempty on every field for Go (a zero value, an empty string, false or an empty list is then left out when the struct is written back to JSON), Check each value’s type while reading (raises TypeError) for Python, and a Package field for Go, Java and Kotlin — Namespace for C# — that puts the declaration where that language expects it. Zod shows its own five in place of the four above: string formats (.email(), .url(), .datetime(), .uuid()) where every sample value agrees, a mixed array as z.tuple([...]), a sometimes-null field as .nullable(), .int() for whole numbers (on from the start), and z.enum or z.literal for strings that keep repeating. Rust structs and enums come with the use serde::{Deserialize, Serialize}; line their derives need. The language you pick is kept in the address — choosing Go writes ?lang=go — so the page’s address opens on it when shared. Under the code a line reminds you the types are a guess from this sample: a name such as Item2 means another shape had already taken that name, a list’s type name is a guessed singular (posts → Post), and a field missing from the sample is not there at all.