Generate TypeScript interfaces or type aliases from strict JSON examples. Object arrays are merged, fields missing from some items can become optional, unsafe property names are quoted, and everything runs locally in your browser.
Continue with a related workflow or open the next tool that usually follows this task.
Use this workflow to turn a representative API response into a useful TypeScript starting point without pretending that one payload is the complete contract. It combines strict JSON cleanup, several array samples, explicit inference review, compilation in the target project, and runtime validation at the network boundary.
OpenRelated toolBeautify or minify strict JSON locally while preserving duplicate keys and number text.
OpenRelated toolTest RFC 9535 JSONPath filters, slices, and selectors against JSON in your browser.
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OpenPaste one strict JSON value or load the sample.
Enter a PascalCase root name such as ApiResponse.
Choose interface or type declarations and optional or readonly property behavior.
Generate the TypeScript and review warnings, unions, empty arrays, nulls, and optional fields.
Copy or download the declarations, then compare them with the real API contract and add runtime validation.
Create a first draft of request and response declarations while integrating a REST or GraphQL endpoint.
Describe fixture and mock payloads consistently before adding them to tests or Storybook stories.
Turn a configuration example into a readable TypeScript shape for application code and review.
Compare several array records to spot fields that are absent, nullable, or represented with conflicting value kinds.
One object cannot show whether a field is truly optional. Optional markers are inferred only when object samples in the same array omit that field; confirm the contract with API documentation or a schema.
An empty array contains no evidence about its element type, so the generator uses Array<unknown>. Replace unknown only after checking a real payload or authoritative schema.
Every JSON number maps to TypeScript number, but long integers and high-precision decimals may not be represented exactly at runtime. Use strings for exact identifiers and decimal libraries where precision matters.
Generated declarations describe the sample shape; they do not validate untrusted data at runtime. Add a schema validator or explicit checks at the network boundary.
Keys that are not valid TypeScript identifiers are quoted, while nested objects receive deterministic declaration names.
{
"id": 42,
"user-name": "Ada",
"profile": {
"display name": "Ada Lovelace"
}
}export interface ApiResponse {
id: number;
"user-name": string;
profile: ApiResponseProfile;
}
export interface ApiResponseProfile {
"display name": string;
}Object samples in one array are merged. Fields absent from some items become optional when optional inference is enabled.
{
"users": [
{ "id": 1, "name": "Ada" },
{ "id": 2, "active": true }
]
}export interface Generated {
users: Array<GeneratedUsersItem>;
}
export interface GeneratedUsersItem {
id: number;
name?: string;
active?: boolean;
}The source must be strict JSON with one root value. Comments, trailing commas, duplicate keys, malformed escapes, and more than 64 nesting levels are rejected instead of silently repaired.
Object arrays are merged by property name. Missing properties can become optional, and values with different JSON kinds become TypeScript unions. Empty arrays use unknown because their element type cannot be proven.
Valid ASCII property identifiers are emitted directly. Other keys are serialized as quoted string properties, while nested declaration names are generated deterministically and disambiguated when names collide.
The tool limits input, output, nesting, and node count. JSON numbers map to number, with a warning when the source literal cannot be represented exactly by a browser number. Static output still requires runtime validation for untrusted data.
Objects use the selected declaration style. A scalar or array root must use a type alias because an interface can describe an object shape but cannot directly alias string, null, or an array.
All object samples in the same array are merged. A property missing from at least one item receives ? when optional inference is enabled; conflicting value kinds become a union.
The generator uses Array<unknown> and shows a warning. An empty sample provides no trustworthy evidence for string, number, or an object shape.
Keys such as user-name, 123, spaces, line breaks, and non-ASCII names are emitted as quoted string properties. This keeps the generated TypeScript syntax valid without changing the original JSON key.
No. The declarations describe the example but do not check data at runtime. Validate external input with a schema library or boundary checks before treating it as the generated type.
Yes. Parsing and type generation run in the browser. Use a redacted representative sample anyway, especially when production payloads contain secrets or personal data.
Maintained and tested by SimpleWebUtilsReviewed
Method: For “Merge two user records into one response shape”, we entered the documented fixture in JSON to TypeScript Interface & Type Generator and followed “Validate the source as strict JSON” before “Generate from several representative records”. We compared the browser result with the stated output, then reviewed “Using production secrets as a convenient sample” and “Inferring optional fields from one object” as separate failure boundaries.
Expected result: The two sample records merged into one users item interface with required id and optional name and active fields, rather than treating the first object as the entire schema.
Open the tested workflowUse these focused guides when you need a practical workflow before opening the tool.
Use this workflow to turn a representative API response into a useful TypeScript starting point without pretending that one payload is the complete contract. It combines strict JSON cleanup, several array samples, explicit inference review, compilation in the target project, and runtime validation at the network boundary.
Workflow guideHTML-to-JSX conversion removes repetitive syntax work, but migration quality depends on what happens afterward. This workflow records the original behavior, limits the conversion to one coherent fragment, compares browser-normalized structure, rewrites legacy events and URLs, moves styles and assets into the destination project, and finishes with lint, type, accessibility, responsive, and security checks. The generated JSX is treated as reviewable source, not as a sanitized or complete component.
Continue with another maintained workflow
Beautify or minify strict JSON locally while preserving duplicate keys and number text.
Test RFC 9535 JSONPath filters, slices, and selectors against JSON in your browser.
Convert JSON records to stable, protected CSV entirely in your browser.
Validate strict JSON locally with exact syntax locations and duplicate-key warnings.
Convert JSON and YAML locally with strict syntax, loss checks, and bounded YAML feature handling.