Free JSON to TypeScript Interface Generator Online

A JSON to TypeScript interface generator takes a raw JSON payload and produces the matching TypeScript interface, including generated types for nested objects and arrays, so you don't have to hand-type field names and types from scratch every time you're integrating a new API response. Paste JSON into the left pane of this tool and a TypeScript interface appears on the right instantly, updating as you edit, with toggles to control export syntax, optional fields, type-alias output, and readonly modifiers.

How This JSON to TypeScript Interface Generator Works

Paste or type JSON into the input pane, and the tool parses it as you go — a green checkmark confirms valid JSON, while a red error message shows exactly what's wrong if the parser can't read it. The generated interface appears in the output pane the moment the input parses successfully, with no separate "convert" button to click. A "Root name" field lets you set what the top-level interface is called instead of a generic default, and four toggles shape the output, covered in more detail below. A copy button places the result on your clipboard, and a download button saves it as a .ts file.

Why Convert JSON to TypeScript

Typing out interfaces by hand is tedious enough that most developers only do it when a shortcut isn't available. A few situations make that shortcut worth reaching for:

• Typing a third-party API response you don't control. When you're consuming an external API with no official TypeScript types, generating an interface from an actual sample response gets you compile-time safety without maintaining hand-written types against documentation that might drift out of date.
• Bootstrapping types during initial integration. Early in building a feature against a new endpoint, generating a starting interface from one real payload is faster than reading through backend code or docs to piece the shape together field by field.
• Keeping test fixtures aligned with real interfaces. Pasting a sample of your mock JSON test data through the generator gives you a quick sanity check that your fixtures still match the shape your code expects, especially after a backend change.
• Documenting a webhook payload for teammates. Converting a captured webhook body into a readable interface communicates its shape more precisely than a JSON dump or a written description, and it's ready to paste straight into a shared types file.
• Sanity-checking nested structure before writing consumption code. Seeing the generated child interfaces makes it obvious how deep a payload's nesting actually goes before you start writing the code that reads it, which saves a round of console-logging the raw object first.
• Sharing a consistent type across a monorepo package boundary. When a frontend package consumes JSON produced by a backend package in the same repository, generating an interface from a real sample and dropping it into a shared types package keeps both sides working from the same shape without duplicating field definitions by hand in two places.

What Each Option Actually Changes

The "Export" toggle prefixes every generated interface with the export keyword, which matters the moment you plan to paste the result into a shared types file that other modules import from — leave it off if you're just pasting the interface directly above the function that uses it in the same file. "Optional" appends a question mark to every single field at once, which is a reasonable starting point for typing an API response where you're not fully certain every field is guaranteed to be present, though it applies uniformly rather than letting you mark only some fields optional — you'll still need to manually remove the question mark from fields you know are always present. "Use type" swaps the output from interface syntax to a type-alias assignment instead; reach for it if your project's lint rules prefer type aliases over interfaces, or if your root JSON value is an array or primitive rather than an object, which is covered in more detail below. "Readonly" prefixes every field with the readonly modifier, which is useful when the generated shape represents immutable state — a Redux store slice or React props object you don't want a stray assignment to mutate by accident.

A Syntax Quirk with Non-Object Root Values

Most JSON payloads people paste in are plain objects, but it's worth knowing what happens if yours isn't. When the root value you paste is a bare array or a primitive value — a raw number, string, or boolean at the top level rather than a JSON object — the browser tool's output still uses whichever keyword the "Use type" toggle currently selects. With "Use type" switched off, that means the tool emits the word "interface" followed by an equals-sign assignment, which isn't valid interface syntax in TypeScript at all; interfaces don't support an assignment form. Turning "Use type" on for a non-object root fixes this immediately, since a type alias is exactly the correct construct for naming an array or primitive type. If you regularly convert payloads whose root is an array of records rather than a single object, it's worth leaving "Use type" on by default rather than discovering the mismatch after pasting invalid output somewhere.

How Nested Objects and Arrays Are Typed

Nested data is where interface generators differ most, and it's worth understanding exactly how this one handles it. For a nested object value, the browser tool creates a separate named interface — a property called "address" generates its own "Address" interface, referenced by name from the parent rather than written inline. For an array whose elements are objects, it names the generated item interface with an "Item" suffix, so a "tags" array of objects becomes a "TagsItem" interface referenced as an array of that type. For an array of primitive values, the browser tool types the whole array using whichever type the first element happens to be — if that array actually mixes types, later elements don't get reflected in the output type, so it's worth spot-checking mixed arrays in your source data before trusting the result blindly. An empty array, with no elements to sample a type from at all, falls back to a generic "any" array type in the browser tool.

The API endpoint documented at /docs takes a different approach to all three of these cases. Rather than generating separate named interfaces for nested objects, it inlines the nested type directly inside the parent interface's body. For arrays that mix primitive types, it doesn't just grab the first element's type — it collects every distinct type actually present in the array and emits a real TypeScript union, such as a parenthesized string-or-number union, so mixed-type arrays are represented accurately rather than approximately. And an empty array comes back typed as an "unknown" array rather than "any," which is a meaningfully safer default since it forces you to narrow the type before using any element from it. Each call to that endpoint uses one credit and accepts a custom root name the same way the browser tool does.

Case	Browser Tool	API Endpoint
Nested object	Separate named interface	Inline nested type
Array of objects	Named "Item"-suffixed interface	Inline element type
Mixed-type primitive array	Typed by first element only	Real union type
Empty array	Typed as "any[]"	Typed as "unknown[]"

JSON to TypeScript Interface Generator vs. Manual Typing

Writing interfaces by hand gives you full control — you can name every field exactly as you'd like, add documentation comments, and use more precise types than a generator can infer from a single JSON sample, such as string literal unions or branded types that don't exist in the raw data at all. That precision comes at a real time cost for large or deeply nested payloads, where hand-typing forty fields across several nested objects invites typos and mismatched property names that a generator sidesteps entirely by reading the actual data instead of retyping it from memory.

Standalone JSON-to-TypeScript utilities built into IDE extensions offer similar convenience without leaving your editor, which is a genuine advantage if you already have one installed and configured. The tradeoff is that a browser-based generator works anywhere, without an extension, the moment you have a JSON sample in hand — reviewing a payload from documentation, a support ticket, or a teammate's Slack message doesn't require your IDE to be open at all.

Privacy and Processing

The JSON you paste and the TypeScript it generates stay entirely within your browser tab for the free tool — nothing is sent to a server to produce the result you see. That's particularly useful if the payload you're typing represents an unreleased API, an internal service contract, or any other schema you'd rather not transmit to a third party just to get a starting interface.

Common Questions About Generating TypeScript from JSON

Does it generate a union type for an array mixing strings and numbers?

The browser tool does not — it types the array using the first element it encounters. The API endpoint does generate a proper union type covering every distinct type actually present in the array.

Will it produce string literal types or enums instead of plain string fields?

No. Every string value is typed as the generic string keyword rather than a literal union or enum, regardless of how few distinct values actually appear in your sample.

How does the tool name nested interfaces?

A nested object takes a capitalized version of its property key as the interface name, and an array of objects gets an "Item"-suffixed name derived the same way.

Can I generate a type alias instead of an interface?

Yes — the "Use type" toggle switches the output from interface syntax to a type-alias assignment. Turn it on if your root JSON value is an array or a primitive rather than an object, since interface syntax isn't valid for those root shapes.

How does the tool type an empty array?

The browser tool falls back to a generic "any" array type when there are no elements to sample. The API endpoint uses "unknown" instead, which is a safer default that requires narrowing before use.

Does the tool validate my JSON before converting it?

Yes. Invalid JSON shows a parser error message directly below the input pane instead of producing a broken or partial interface.

Can I mark every generated field as optional in one step?

Yes — the "Optional (?)" toggle appends a question mark to every field at once, rather than requiring you to edit each one individually afterward.

Related Tools

Before converting, running your payload through the JSON validator confirms it parses cleanly, and the JSON formatter re-indents a minified or messy sample so it's easier to read while you sanity-check the structure. If you need to see every field's exact path within a deeply nested payload, the JSON path finder lists them individually, and once you're done inspecting a sample, the JSON minifier strips it back down for storage or transmission.