---
id: built-in-types
title: Built-in types
---

# Built-in Types

TypeSpec Standard Library provide some built-in types that can be used to build more complex types.

Built in types are related to each other according to the rules described in [type relations](../language-basics/type-relations.md).

## Numeric types

| Type         | Range                                                                                                        | Description                               |
| ------------ | ------------------------------------------------------------------------------------------------------------ | ----------------------------------------- |
| `numeric`    |                                                                                                              | Parent type for all numeric types         |
| `integer`    |                                                                                                              | A whole-number                            |
| `float`      |                                                                                                              | A binary number                           |
| `int64`      | `-9,223,372,036,854,775,808` to `9,223,372,036,854,775,807`                                                  | A 64-bit integer                          |
| `int32`      | `-2,147,483,648` to `2,147,483,647`                                                                          | A 32-bit integer                          |
| `int16`      | `-32,768` to `32,767`                                                                                        | A 16-bit integer                          |
| `int8`       | `-128` to `127`                                                                                              | A 8-bit integer                           |
| `safeint`    | <code>−9007199254740991 (−(2<sup>53</sup> − 1))</code> to <code>9007199254740991 (2<sup>53</sup> − 1)</code> | An integer that can be serialized to JSON |
| `uint64`     | `0` to `18,446,744,073,709,551,615`                                                                          | Unsigned 64-bit integer                   |
| `uint32`     | `0` to `4,294,967,295`                                                                                       | Unsigned 32-bit integer                   |
| `uint16`     | `0` to `65,535`                                                                                              | Unsigned 16-bit integer                   |
| `uint8`      | `0` to `255 `                                                                                                | Unsigned 8-bit integer                    |
| `float32`    | <code> ±1.5 x 10<sup>45</sup></code> to <code>±3.4 x 10<sup>38</sup></code>                                  | A 32 bit floating point number            |
| `float64`    | <code>±5.0 × 10<sup>−324</sup></code> to <code>±1.7 × 10<sup>308</sup></code>                                | A 64 bit floating point number            |
| `decimal`    |                                                                                                              | A decimal number                          |
| `decimal128` | 34 decimal digits with an exponent range from `-6143` to `6144`                                              | A 128 bit decimal number                  |

## Date and time types

| Type             | Description                                                                         |
| ---------------- | ----------------------------------------------------------------------------------- |
| `plainDate`      | A date on a calendar without a time zone, e.g. "April 10th"                         |
| `plainTime`      | A time on a clock without a time zone, e.g. "3:00 am"                               |
| `utcDateTime`    | A date and time in coordinated universal time (UTC), e.g. "1985-04-12T23:20:50.52Z" |
| `offsetDateTime` | A date and time in a particular time zone, e.g. "April 10th at 3:00am in PST"       |
| `duration`       | A duration/time period. e.g 5s, 10h                                                 |

## Other core types

| Type        | Description                                                                                                                                            |
| ----------- | ------------------------------------------------------------------------------------------------------------------------------------------------------ |
| `bytes`     | A sequence of bytes                                                                                                                                    |
| `string`    | A sequence of textual characters                                                                                                                       |
| `boolean`   | Boolean with `true` and `false` values                                                                                                                 |
| `null`      | Null value                                                                                                                                             |
| `Array<T>`  | Array model type, equivalent to `T[]`                                                                                                                  |
| `Record<T>` | Model with string keys where all the values have type `T` (similar to `Map<string, T>` in TypeScript or `Dictionary<string, T>` in .Net)               |
| `unknown`   | A top type in TypeSpec that all types can be assigned to. Values that can have any type should be assigned this value (similar to `any` in JavaScript) |
| `void`      | A function/operation return type indicating the function/operation doesn't return a value.                                                             |
| `never`     | The never type indicates the values that will never occur.                                                                                             |

## String types

Built-in types that are known string formats

| Type  | Description  |
| ----- | ------------ |
| `url` | A url String |
