Explore real-world developer payloads and load them instantly into the editor.
A standard Stripe payment event payload with nested object structures.
A typical GitHub REST API user profile response for public profile data.
A complex nested weather API response with coordinate and system objects.
A Slack Block Kit message payload with nested blocks and accessory elements.
Simply paste your raw JSON string or API payload into the left input window pane. The online compiler engine instantly evaluates the nested object shapes and outputs copy-pasteable TypeScript interfaces in real-time.
Both represent structural layout patterns in TypeScript. However, interfaces can be extended using 'extends' and allow declaration merging, making them ideal for modeling dynamic backend API response payloads.
Click the 'Copy' pill module to store the compiled schema string in your clipboard. Paste it directly into your .ts files inside VS Code. Tip: You can turn on our optional parameters button (?) to make all property fields safely optional to prevent build errors.
If an input array contains varying primitives (e.g., strings and numbers), the client-side syntax compiler infers a union type array shape, automatically rendering the structure as (string | number)[] instead of falling back to any[].
Working with REST APIs, GraphQL responses, or mock JSON payloads means dealing with raw, untyped data structures every single day. Manually writing TypeScript interfaces for every API response is tedious, error-prone, and slows down your development workflow. Fast JSON to TypeScript eliminates that friction entirely — paste your JSON, get production-ready TypeScript interfaces in milliseconds, right in your browser.
The conversion engine runs 100% client-side using a recursive type inference algorithm written in vanilla JavaScript. When you paste a JSON string into the left editor pane, the parser walks every key-value pair in your payload. Primitive values — strings, numbers, booleans, and nulls — map directly to their TypeScript equivalents. Nested objects are recursively expanded into inline interface shapes. Arrays are inspected for element type consistency: a uniform array becomes string[], while a mixed-type array automatically infers a union type such as (string | number)[] instead of falling back to any[].
The result is rendered on the right pane with full VS Code–style syntax highlighting — keywords in blue, type names in teal, strings in orange — so the output feels native to your IDE before you even paste it in.
Real-time conversion. The output updates on every keystroke — no buttons to click, no round trips to a server. The tool uses CodeJar, a 2KB micro-editor, combined with PrismJS for syntax highlighting, keeping the page load under 50KB total.
snake_case to camelCase transformation. Backend APIs frequently use snake_case naming conventions (e.g. user_id, created_at), while TypeScript codebases prefer camelCase. Toggle the conversion option and all field names are automatically transformed.
Optional fields toggle. When working with partial API responses or nullable fields, enable the optional fields mode. Every property in the generated interface gets a ? suffix, preventing TypeScript compilation errors when response fields are absent.
One-click clipboard copy. Hit the Copy button and the full TypeScript output is written to your clipboard, ready to paste directly into your .ts files in VS Code, WebStorm, or any other editor.
The converter outputs an interface declaration for top-level JSON objects because interfaces support declaration merging and the extends keyword, making them the idiomatic choice for modeling API response shapes. When the root JSON value is a primitive or an array, the tool falls back to a type alias, which is the correct TypeScript construct for those cases.
This tool is built for frontend and full-stack developers who work with typed JavaScript every day. Common workflows include: converting Stripe webhook event payloads into typed interfaces before integrating billing logic; generating TypeScript types from GitHub API responses when building developer tooling; typing OpenWeatherMap and other third-party API responses to eliminate any from your data fetching layer; and scaffolding interface definitions from mock JSON fixtures during test-driven development.
Unlike server-based converters, this tool performs all parsing and type inference locally in your browser tab. Your JSON payloads — which may contain sensitive API keys, user records, or internal data structures — are never transmitted to any server. The page has no backend, no analytics on your input, and no cookies tied to your conversion history. It is a zero-overhead, zero-trust developer utility designed to work offline once the page has loaded.