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Type helper

JSON to TypeScript types

Paste any JSON and instantly generate a TypeScript type definition.
Objects and arrays are inspected to infer field names and nested shapes,
so you can drop the output straight into your codebase.

Nothing is sent to a server—parsing and type generation run entirely in your browser.

Guide: How to use & features

  • Paste JSON into the input and click “Convert to TypeScript.”
  • Objects are formatted into a structured block with typed properties.
  • Arrays are analyzed to determine element types; mixed content becomes a union.
  • Use the copy or clear buttons to reuse the output or start over.

Samples: Sample input & output

Generate TypeScript types

Input

{"title":"Draft","tags":["dev","web"],"stats":{"views":1200}}

Output

type Root = {
    title: string;
    tags: string[];
    stats: {
        views: number;
    };
};

FAQ: FAQ

  • Are optional and nullable fields inferred correctly?

    Types are inferred from the JSON sample you paste, so any key present in the sample is emitted as required. For fields that can actually be omitted, add a ? after generation to make them optional, and add `| null` to fields that can be null, so the type matches your real data.

  • How are nested objects and arrays converted?

    Nested objects expand into nested types (interfaces), and arrays are inferred as `T[]` from their element type. The more uniform the array elements, the more accurate the resulting type.

  • What happens when an array mixes different element types?

    Mixed elements produce a union type (for example `(string | number)[]`). If that yields a wider type than you want, regenerate from a sample narrowed to one representative item to get the type you intended.

Use cases: Common use cases

  • Bootstrapping type definitions

    Generate TypeScript interfaces from sample backend responses to kick off a type-safe implementation quickly.

  • Aligning contracts

    Turn shared JSON into types to clarify expectations about field names, optional flags, and shapes.

  • Lightweight review snippets

    Produce minimal interfaces you can paste into PR comments to focus discussion on structure over typos.

Notes: Notes & limitations

  • Work stays in your browser

    Inputs and outputs remain local. Closing the tab or clearing cache will remove any temporary state.

  • Validate critical data

    Results are helper outputs—double-check them before sending to production systems or sharing externally.

  • Large payloads depend on your device

    Very large text or files can feel slow in some browsers. Use a desktop environment for heavy workloads.

JSON to TypeScript Type & Interface Generator

Automatically generate TypeScript interface and type definitions with just one click by parsing sample JSON responses or dummy data payloads.
This drastically cuts down the hours spent manually writing type definition files required for strict type enforcement in modern frontend development frameworks (like Next.js, React, or Vue). It seamlessly parses deeply nested objects and arrays, integrating smoothly into your secure, local workflow.

Common use cases

  • Type API responses: Paste a real response body and create a starting point for frontend types.
  • Document payload shape: Turn sample JSON into readable TypeScript definitions for teammates.
  • Speed up prototyping: Generate temporary interfaces while exploring unfamiliar APIs.

Review before production

Generated types are inferred from the sample you provide. If an API can return optional fields, nullable values, mixed arrays, or error responses, review the generated result and adjust it to match the real contract.

Articles for this tool

Introduction
2026-01-11

How to Generate TypeScript Types from JSON: A Hands-On Guide with Examples

Turn API-response JSON into type-safe TypeScript interfaces. Real conversion examples covering null, arrays, nesting, naming tips, and when to hand-edit.

Introduction
2026-05-02

JSON Formatting and Validation: How to Read API Responses Safely

Learn how to format JSON, catch syntax errors, inspect value types, and turn API responses into types, schemas, or documentation.

Introduction
2026-02-16

The JSON Ecosystem: Connecting Formatting, Types, Validation, and API Specs

Follow one API response through formatting, TypeScript types, Zod runtime validation, and OpenAPI definitions—with real code at every step—for a clear view of type-safe API development.

Recent Articles

Use Case
2026-08-07

curl Options Cheat Sheet: What -X, -H and -d Actually Do

A reference for the curl options you meet in real API work: why -d already implies POST, how -d differs from --data-raw, the @ prefix that silently reads a file, single vs double quotes, and why -k and -L deserve more caution than they usually get.

Introduction
2026-08-06

Converting Between JSON Schema and Zod: How required Maps to .optional()

Inside a two-way converter that turns JSON Schema into a Zod schema and Zod code back into JSON Schema. Covers the inverted defaults between required and .optional(), the constraint mapping table, and how the Zod side is parsed without executing any code.

Use Case
2026-08-06

SQL Clause Order Reference: Why WHERE Can't See Your SELECT Alias

The order you write SQL clauses is not the order the database runs them. A reference for the logical execution order (FROM → WHERE → GROUP BY → HAVING → SELECT → ORDER BY → LIMIT), why aliases fail in WHERE, when to use WHERE vs HAVING, and the MySQL/PostgreSQL differences that bite.

Use Case
2026-08-06

Unified Diff Format Reference: Reading @@ Hunks in git diff Output

How to read the unified diff format git produces: what the four numbers in @@ -12,7 +12,9 @@ mean, why a one-character edit shows as a whole-line replacement, the whitespace and line-ending traps, \ No newline at end of file, combined @@@ diffs on merges, and rename detection via similarity index.

Use Case
2026-08-06

UTC to JST Reference: The 9-Hour Offset, Cheat Sheet & Timezone Pitfalls

Convert between UTC and JST (Japan Standard Time) with a cheat sheet. Covers what Z and +09:00 mean in ISO 8601, when JavaScript date parsing silently shifts by 9 hours, MySQL/PostgreSQL timezone behavior, and why GitHub Actions cron always runs in UTC.

Use Case
2026-08-04

CREATE TABLE Reference: MySQL vs PostgreSQL vs SQLite Types & Constraints

A cross-database CREATE TABLE (DDL) reference with cheat sheets for data types, auto-increment keys (AUTO_INCREMENT / IDENTITY / rowid), foreign key ON DELETE behavior, and the CHECK constraint that MySQL silently ignores.

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