---
title: String Built-ins
sidebar_label: Strings
---

<BuiltinTable category={"strings"}/>

:::info
When using `sprintf`, values are pre-processed and may have an unexpected type. For example,
`%T` evaluates to `string` for both `string` and `boolean` types. In such cases, use `type_name` to
accurately evaluate the underlying type.
:::

## Examples

### `contains`

`contains` is a commonly used Rego built-in function that checks if a string contains a substring. The function returns `true` if the string contains the substring and `false` otherwise.

Some examples of policy use cases where `contains` might be used include:

- Simple validation, such as checking if an email contains a `@` symbol.
- Checking if user input contains restricted words or phrases for content moderation.

:::caution

If you're looking to check a string that's expected to be at the start or end of a value, you might be better served by one of the following functions:

- [Starts With](#builtin-strings-startswith): Checks if a string starts with a specified prefix.
- [Any Prefix Match](#builtin-strings-stringsany_prefix_match): Checks if a string starts with any of the specified prefixes.
- [Ends With](#builtin-strings-endswith): Checks if a string ends with a specified suffix.
- [Any Suffix Match](#builtin-strings-stringsany_suffix_match): Checks if a string ends with any of the specified suffixes.

These are safer and potentially faster too.
:::

:::danger
`contains` only operates on strings, if you're looking to check for the presence of a value in a list you cannot use this function.
:::

:::note
If you're looking for the Rego keyword `contains` for building multi-value rules, you can read
about it in the [keywords section](/docs/policy-reference/keywords/contains).
:::

<PlaygroundExample dir={require.context('../_examples/strings/contains/email-validation')} />

<PlaygroundExample dir={require.context('../_examples/strings/contains/content-moderation')} />
