JSON to TypeScript Interface
Generate TypeScript interfaces from a JSON sample instantly in your browser — infers types for nested objects and arrays so you don't have to type them by hand.
What Is JSON-to-TypeScript Conversion?
TypeScript describes the shape of your data with interfaces — named definitions listing each field and its type. When you're working with a JSON API response, a config file, or a data sample, writing that interface by hand means manually reading through the JSON and typing out every field, one at a time.
This tool automates that: it looks at a real JSON sample, infers a type for every value (string, number, boolean, nested object, array), and generates the matching TypeScript interface definitions for you.
Why Generate Types From JSON?
Typing an interface by hand is slow and error-prone, especially for a deeply nested API response with dozens of fields. Generating it from a real example is faster and guarantees the field names and basic types actually match your data — no any scattered through your code because typing it all out felt like too much effort.
How This Tool Works
Paste a JSON sample into the box below and click Generate Interface. This tool walks the structure, creates a named interface for every nested object, and infers array element types from the first item. Everything runs in your browser; nothing is uploaded to any server.
Hand-Written vs. Generated TypeScript Interfaces
| Feature | Hand-Written | Generated From JSON |
|---|---|---|
| Speed | Slow for large/nested objects | Instant |
| Accuracy | Prone to typos, missed fields | Matches the actual sample exactly |
| Nested objects | Requires manually naming each one | Automatically named and split out |
| Best for | Types that need business logic beyond raw shape (unions, optional fields you know about but the sample doesn't show) | A fast starting point from a real example |
Write Interfaces by Hand When
- You need fields marked optional (
?:) that don't appear in every response - You want precise union types (
"admin" | "user") instead of a plainstring - The type needs to encode business rules the JSON sample alone can't show
Generate From JSON When
- You have a real example response and want a fast, accurate starting point
- You're prototyping and just need something usable now, refinable later
- You're documenting an API's actual shape rather than its idealized one
Common Scenarios for Generating TypeScript from JSON
Typing an API Response Before Writing Client Code
Before you write the code that consumes an API, pasting a real response here gives you a starting interface immediately — no guessing at field names or types while you write the rest of your integration.
Documenting a Data Export or Webhook Payload
If a script or service produces a JSON manifest — for example, a list of files generated by a batch job like our PDF Merge tool — typing that manifest's shape makes it easier for other code (or teammates) to consume it safely.
Prototyping With Sample Data
When building a feature against mock or sample JSON before the real API exists, generating a type from the mock gives your prototype the same type-safety benefits as the finished integration, without hand-writing the interface twice.
Reviewing an Unfamiliar API's Shape
Third-party APIs don't always publish TypeScript types. Pasting a sample response here gives you a quick, readable view of the actual structure — nested objects and array item shapes included — without digging through documentation.
Catching Field Name Typos Early
Hand-typing long interfaces invites typos in field names that TypeScript won't catch (a misspelled optional-looking property just becomes undefined silently). Generating the interface from the real JSON removes that entire category of mistake.
Other Ways to Generate TypeScript from JSON
You can also generate TypeScript types from JSON using a code editor extension, or the quicktype command-line tool. FileCast is useful for a quick, one-off conversion without installing anything.
Frequently Asked Questions
Is my JSON uploaded anywhere?
No. Generation happens entirely in your browser — nothing is uploaded to any server.
How are nested objects named?
Each nested object gets an interface named after its property key (for example, an address field becomes an Address interface). If two different nested objects would generate the same name, a number is appended to keep them distinct.
How does this handle arrays?
Array types are inferred from the first element only. If your JSON has an array of objects, the tool generates one interface from the first item's shape and types the array as that interface's plural (Item[]). If later items in the array have different fields, those won't be reflected — check the output against your full dataset for critical use cases.
Are any fields marked optional?
No. Every field in the generated interface is required (no ?:), since a single JSON sample can't show which fields are sometimes missing. If you know a field is optional from context, add the ? by hand after generating.
What if my top-level JSON is just a number, string, or array of primitives?
The tool still generates a valid type RootObject = ...; alias — for example, type RootObject = string[]; for a plain array of strings — rather than requiring the root to be an object.