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Utility Type Helper

A complete, searchable reference and live generator for every built-in TypeScript utility type. Pick a utility and a base type, fill in its arguments, and instantly get the applied alias, a realistic before/after example, and the equivalent hand-written mapped/conditional implementation so you learn how it works. Search by name or by what you want to do (e.g. 'make optional' finds Partial).

About this ToolHow it works, benefits & use cases

A complete, searchable reference and live generator for every built-in TypeScript utility type. The catalogue covers the object reshapers (Partial, Required, Readonly, Pick, Omit, Record), the union filters (Exclude, Extract, NonNullable), the function and constructor extractors (Parameters, ConstructorParameters, ReturnType, InstanceType, ThisParameterType, OmitThisParameter), the Promise unwrapper (Awaited), the inference guard (NoInfer), and the string-literal casing intrinsics (Uppercase, Lowercase, Capitalize, Uncapitalize). Every entry shows its signature, a plain-English description, a worked example, and — crucially — the equivalent hand-written mapped or conditional type, so you can see that Partial is just { [K in keyof T]?: T[K] } and ReturnType is an infer inside a conditional type. The interactive builder lets you pick a utility, type a base type and its arguments (keys for Pick/Omit, union members for Exclude/Extract, key and value types for Record), and instantly get the applied alias plus a realistic before/after snippet. You can search the catalogue by name or by intent — typing 'make optional' surfaces Partial, 'remove key' surfaces Omit, 'unwrap promise' surfaces Awaited — and the whole configuration lives in a shareable URL.

How to Use

  1. 1Pick a utility from the Builder dropdown, or search the catalogue by name or by what you want to do.
  2. 2Enter a base type (a bare function/class name is automatically wrapped in typeof for ReturnType, Parameters, InstanceType, etc.).
  3. 3Fill in the utility-specific arguments: a comma-separated key list for Pick/Omit, union members for Exclude/Extract, or a key type and value type for Record.
  4. 4Read the generated export type alias and the equivalent hand-written implementation in the live output panel.
  5. 5Study the before/after example and the catalogue description to confirm the transformation does what you expect.
  6. 6Copy, download, or share the result — the URL captures the utility, base type, and all arguments.

Key Benefits

  • Documents every built-in utility type, not just the common six — including ConstructorParameters, ThisParameterType, OmitThisParameter, and NoInfer
  • Shows the equivalent hand-written mapped/conditional implementation so you learn how each utility actually works
  • Searchable by intent: "make optional", "remove key", "unwrap promise" map to the right utility
  • Interactive builder emits a clean, named export type alias with a realistic before/after example
  • Automatically wraps function and class names in typeof for the extractor utilities
  • Grouped catalogue (object, union, function, async, string, inference) for fast browsing
  • Runs entirely in the browser with a shareable URL and no upload

Common Use Cases

  • Deriving a PublicUser from a User interface by omitting the password field
  • Building an all-optional update payload type with Partial
  • Creating a strongly-typed lookup with Record<Page, PageInfo>
  • Extracting a function's return type with ReturnType<typeof getUser> instead of duplicating it
  • Filtering a string-literal union down with Exclude or Extract
  • Learning the mapped-type internals behind Pick, Readonly, Required, and the conditional-type internals behind ReturnType and Awaited
Omit<Type, Keys>object

Applied alias + equivalent implementation

export type OmitUser = Omit<User, 'password'>;

// Equivalent hand-written implementation:
type MyOmit<T, K extends keyof any> = Pick<
  T,
  Exclude<keyof T, K>
>;

Before / after example

// Source type: User

// Omit removes: password
export type OmitUser = Omit<User, 'password'>;
What Omit does

Constructs a type by removing the set of properties Keys from Type (the inverse of Pick).

Builder

Each key is quoted and joined with |.

Catalogue

Object types

Union types

Function & constructor types

Promise / async

String literal types

Inference control

A reference you can actually run

TypeScript ships a couple dozen built-in utility types that transform existing types. This helper is both a complete catalogue — each with a signature, a plain-English description and a worked example — and a live generator. Pick a utility, give it a base type and its arguments, and it writes the exact export type alias for you.

See how it works under the hood

For most utilities the output also includes the equivalent hand-written mapped or conditional type, so you can see that Partial is just { [K in keyof T]?: T[K] } and ReturnType is an infer in a conditional type. A few string-casing helpers are compiler intrinsics with no userland equivalent, which the tool calls out.

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