⚡ Quick Answer
Step 1
Paste JSON in the left panel
Step 2
Click Convert
Step 3
Copy the generated interface
Nested objects become separate exported interfaces with PascalCase names (e.g. Address for a user.address property). All conversion happens in your browser — your JSON is never sent to a server.
Paste JSON, get matching TypeScript interfaces instantly — free, no signup
Paste any JSON object into the left panel, click Convert, and the tool generates matching TypeScript interfaces with proper types — strings, numbers, booleans, nested objects (as separate exported interfaces), and typed arrays. Copy the result and paste it directly into your TypeScript project.
Manual interface writing is tedious and error-prone. This converter auto-infers types from a real JSON sample, so your types reflect the actual shape of your data — including the nested object structure that hand-written types often miss.
Paste your JSON object into the left textarea and click Convert. The tool generates a matching TypeScript interface (with nested objects as separate interfaces, arrays as typed arrays, and a customizable root name) in the right panel. Click Copy to copy the exported interface into your clipboard, then paste it into your TypeScript project. The whole flow takes about 5 seconds and runs entirely in your browser — no data is sent to any server.
The converter supports all JSON types: string, number (integer and float both map to number in TypeScript), boolean, null (mapped to the literal null), arrays (typed based on the first item's type, e.g. number[] or string[]), and nested objects (each nested object becomes its own exported interface with PascalCase naming based on the property name). For example, a JSON object with a property user.profile.address generates User, Profile, and Address interfaces automatically.
Yes. Nested objects are detected recursively and exported as separate interfaces with PascalCase names derived from the parent property name. Arrays of objects become typed arrays of the nested interface (e.g. Item[]). Arrays of primitives become string[], number[], or boolean[]. The converter handles unlimited nesting depth — for example, a JSON payload with user.posts.comments.author generates User, Post, Comment, and Author interfaces all linked by reference.
Yes, completely free with no signup, no account, no usage limits, and no ads interrupting the workflow. The tool runs entirely in your browser using a small JavaScript inference engine — your JSON is never sent to a server, never logged, and never stored. It's the same privacy posture as a desktop developer tool.
Yes. The Root Interface Name field (top-left of the converter) lets you set any name for the top-level interface. The default is Root. For example, if your JSON represents a User object, type User in the field and the exported interface becomes export interface User instead of export interface Root. The field updates the output instantly when you click Convert.
The current version emits all properties as required by default, which matches the most common pattern for TypeScript API types. If your JSON samples have inconsistent shapes (some properties missing across multiple objects), paste the most complete sample to get accurate required types. For nullable fields (where a value is null in your JSON), the tool emits the literal type null, so you'll want to widen those to string | null or use the optional modifier manually after export.
A JSON property whose value is null becomes the literal type null in the generated interface (e.g. middleName: null;). A missing property (not present in the JSON at all) is omitted from the interface. After export, you can broaden null to its union type (string | null), or add the ? modifier to make the field optional. This split is intentional: it gives you precise literal types you can edit rather than guessing.
No. The converter runs entirely client-side in your browser using a local JavaScript type-inference function. The JSON you paste never leaves your machine, is not logged anywhere, and is not transmitted over the network. You can verify this by opening the page, disconnecting from the internet, and using the converter — it still works because there are no server roundtrips.
TypeScript brings compile-time type safety to JavaScript. When you have JSON data from an API, you need TypeScript types (interfaces or types) to use it safely in TypeScript code. Manually writing types from JSON is error-prone: a single missed field causes runtime bugs that TypeScript would have caught at compile time. This tool reads your JSON structure and generates matching TypeScript interfaces, including nested objects and arrays.
TypeScript has two syntaxes for defining types: interface (declaration syntax) and type (alias syntax). Interfaces support declaration merging (you can add fields later), are extendable with extends, and are generally preferred for object shapes. Types support unions, intersections, and computed types — features interfaces don't. Most style guides recommend interface for data shapes and type for unions. Our converter outputs interface by default.
For nested objects (an object containing other objects), the tool generates separate interfaces for each level. For arrays of objects, it creates an array type like User[]. For optional fields (those that appear in some objects but not others), it adds ? to mark them optional. The output is a complete, copy-pasteable TypeScript file you can drop into your project.
Convert JSON objects to TypeScript interfaces automatically with the Toolzie JSON to TypeScript converter. Paste any JSON and get a fully typed TypeScript interface in seconds — a huge time-saver for TypeScript developers.
Yes — nested JSON objects generate nested TypeScript interfaces automatically.
Arrays are typed as the appropriate array type, e.g. string[] or User[].
Null values are typed as the detected type unioned with null, e.g. string | null.
Yes — the generated interfaces are valid TypeScript and can be pasted directly into your .ts or .d.ts files.
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