---
id: built-in-types
title: 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`    | [\*](#numeric-supertypes)                                                                                    | Parent type for all numeric types         |
| `integer`    | [\*](#numeric-supertypes)                                                                                    | A whole-number                            |
| `float`      | [\*](#numeric-supertypes)                                                                                    | 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`    | [\*](#numeric-supertypes)                                                                                    | A decimal number                          |
| `decimal128` | 34 decimal digits with an exponent range from `-6143` to `6144`                                              | A 128 bit decimal number                  |

### Numeric supertypes

`numeric`, `integer`, `float` and `decimal` are types that represent any possible number in their category. For some emit targets, `BigInt` or `BigDecimal` might be an analogous type satisfying the TypeSpec types `integer` and `decimal` respectively. For other targets where the language, serialization format, or protocol does not support an analogous type, emitters may decide on a policy for emitting the numeric supertypes. This might involve picking the closest analogous type and reporting a warning when they are encountered.

## 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                                                 |

:::note

These types do not define any specific serialization format. They represent the concept of time. Each protocol or serialization format should define the default serialization format.

The default encodings for various protocols are defined here:

- [JSON over HTTP](../libraries/http/encoding.md#utcdatetime-and-offsetdatetime)
- [XML](../libraries/xml/guide.md)
  :::

## 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<Element>`  | Array model type, equivalent to `Element[]`                                                                                                                |
| `Record<Element>` | Model with string keys where all the values have type `Element` (similar to `Map<string, Element>` in TypeScript or `Dictionary<string, Element>` 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 |
