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Automatically convert JSON data into TypeScript interfaces or type aliases for frontend data modeling and API integration.
Overview
Understand what the tool solves, how it works, and the boundaries of its data.
Paste valid JSON to generate TypeScript declarations that describe the structure visible in that sample. Nested objects become related declarations; arrays and mixed values inform the inferred types. The root declaration name starts as Root. For example, {"id":7,"tags":["new"],"profile":{"active":true}} can produce a root type with numeric id, string-array tags, and a nested profile shape.
This page accepts a single JSON sample at a time. It does not compare multiple responses or infer a complete API contract. A field absent from this one sample cannot be inferred as optional from comparison with other samples. Empty arrays provide no evidence about element type and can produce a broad type such as any[].
TypeScript declarations help a static checker reason about code. They do not change incoming JSON and do not automatically validate a value at runtime. JSON also has no native date type: a timestamp arrives as a string unless application code parses it. Similarly, a property-name cleanup option can change names in the generated declaration without changing the original object keys.
For richer needs, the options include interface versus type alias, an optional runtime-checking output mode, and language-specific choices. Treat the generated text as a starting point and compare it with the schema or contract that defines valid data.
Guide
Follow the workflow and verify inputs and outputs with practical examples.
Use double quotes around object keys and strings. Remove comments, trailing commas, functions, and JavaScript-only values such as undefined.
Enter one representative object or array and replace Root with a meaningful declaration name such as OrderResponse.
Keep type-only output for declarations, or select type aliases instead of interfaces. The optional runtime-checking output adds code that you should inspect against your project requirements.
Check nested names, arrays, nullable values, date-like strings, and broad types before reusing the result. The generated file uses the declaration name and a TypeScript extension.
For a field that may be missing or may contain null, the single input should show only what it actually contains. Compare several real responses yourself and update the declaration to reflect the contract, including optional properties and union cases.
Use cases
See how the tool fits into real work and everyday tasks.
Paste a representative response to sketch nested response types, then compare every property and variant with the API specification.
Generate a first declaration from a sample fixture or configuration object. Add constraints such as literal unions and required keys from the maintained schema.
Use an observed object shape as a starting point for TypeScript annotations, then expand the examples and refine broad or uncertain types.
Q&A
Find concise answers to common questions and confusing cases.
JSON requires double-quoted keys and strings and does not allow comments, functions, undefined, or trailing commas. Use the strict JSON form before generating declarations.
No. The tool takes one JSON sample per generation. To infer which keys may be absent, compare multiple samples or use the API’s schema and update the declarations yourself.
An empty array contains no example element from which to infer a type. Add a representative non-sensitive element or replace the broad output with the type required by the contract.
Type-only declarations are static information and do not validate a response while a program runs. The optional runtime-checking output is separate code and still needs review and testing in your project.
Notes
Review scope, result limitations, and important precautions before use.
Generated declarations describe observed data. They are not a guarantee that future responses match, nor a substitute for runtime validation.
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