JSON to TypeScript
Generate strongly typed TypeScript interfaces and type aliases from JSON payloads with zero server uploads.
- Runs in your browser
- Free, no signup
export interface Root {
id: number;
name: string;
email: string;
is_admin: boolean;
roles: string[];
profile: Profile;
}
export interface Profile {
bio: string;
reputation: number;
}
Your files are processed locally in your browser and are not uploaded to our server.
Manually writing TypeScript interfaces for complex REST APIs or GraphQL responses is tedious and error-prone. This tool inspects your JSON payload, infers every primitive and composite data type, and generates clean, reusable TypeScript interfaces and type aliases in milliseconds.
Nested objects become dedicated sub-interfaces with unique names, lists are typed as arrays (T[]), and null values are mapped to union types (T | null). Every character of processing happens strictly inside your browser using the local JavaScript engine—no data is ever transmitted across the network, ensuring complete confidentiality for private API keys and sensitive payloads.
How to use this tool
- Paste your JSON payload into the input editor or click "Load Sample" to try an example.
- Specify your desired root model name (e.g., UserProfile or ApiResponse) and select your preferred output style (interface or type alias).
- The converter runs live as you type, reporting exact line and column numbers if syntax errors are detected.
- Click "Copy Code" to copy the generated declarations to your clipboard, or "Download .ts" to save a ready-to-import TypeScript file.
Intelligent Type Inference for Primitives and Collections
The generator distinguishes between strings, numbers (integers and floating-point values), booleans, and nulls. When an array is encountered, the generator inspects its items to determine whether it is a homogeneous list of primitives (such as string[] or number[]) or a collection of complex objects.
Mixed arrays and empty collections are safely typed with unknown or any to prevent runtime type errors while encouraging strict compiler checks in your TypeScript codebase.
Automatic Extraction of Nested Object Interfaces
Rather than generating unwieldy inline object types that clutter your code, the generator extracts each nested JSON object into its own named interface. Interface names are derived from their parent keys using PascalCase conventions (for instance, a "shipping_address" key produces an interface named "ShippingAddress").
Naming conflicts are prevented by appending unique numerical suffixes, ensuring that every interface remains completely self-contained and modular.
Comprehensive Null-Safety and Optional Property Handling
In real-world applications, API endpoints frequently return null or omit fields under certain conditions. The generator detects nullable properties and represents them with explicit union types (such as string | null) and optional property markers (?:).
This matches TypeScript's strictNullChecks compiler flag, ensuring your application code handles missing values gracefully without unexpected runtime errors.
Zero-Upload Privacy and Local Execution
Developers frequently inspect sensitive JSON payloads containing session tokens, internal IDs, customer details, or proprietary business logic. Most web converters send your text to third-party servers for processing.
ToolDuck executes 100% in-browser using client-side JavaScript. Disconnect from the internet or inspect your browser network tab—not a single byte of your data leaves your device.
Frequently asked questions
Can I choose between TypeScript interfaces and type aliases?
Yes. You can toggle between "export interface Name { ... }" and "export type Name = { ... };" directly in the toolbar options. Both formats support nested model extraction and null-safety.
How does the converter handle invalid or malformed JSON?
If your JSON has syntax errors (such as missing closing brackets, trailing commas, or unquoted keys), the editor highlights the exact error line and column with an actionable error banner so you can correct it immediately.
Can I convert an array of JSON objects?
Yes. If your root JSON is an array of objects, the generator inspects the items to generate the model for an individual item and exports an array type (e.g., export type RootList = Root[];).
Is there a limit on JSON payload size?
Because execution takes place in your browser, the tool easily processes payloads of several megabytes without latency or server timeouts.
Is any of my JSON uploaded to a server?
No. Parsing and model inference run completely on your client machine using JavaScript. No payload data is ever logged, stored, or transmitted to any remote server.