> ## Documentation Index
> Fetch the complete documentation index at: https://hellocsv.mintlify.app/llms.txt
> Use this file to discover all available pages before exploring further.

# Validators

This section describes the available validation rules.

## required

**Description:**\
Ensures the field is not empty.

**Additional:**\
Accepts an optional `error` message.
Additionally, accepts a `when` function that returns a boolean value. If the function returns false, the validation is skipped. Defaults to `() => true`.

Example:

```ts theme={null}
{
  "validate": "required",
  "when": (row) => row['employee.type'] === 'other'
}
```

***

## unique

**Description:**\
Ensures the value is unique across rows.

**Additional:**\
Accepts an optional `error` message. Set `caseInsensitive` to `true` to compare
string values case-insensitively.

***

## regex\_matches

**Description:**\
Validates a field against a regular expression.

**Additional:**\
Expects a `regex` and an optional `error` message.

***

## includes

**Description:**\
Checks if a value is within a predefined list.

**Additional:**\
Requires a list of valid values.

***

## multi\_includes

**Description:**\
Checks if all delimited values are valid.

**Additional:**\
Accepts `values`, a `delimiter`, and an optional `error` message.

***

## is\_integer

**Description:**\
Validates that the value is an integer.

**Additional:**\
Optional `error` message.

***

## phone\_number

**Description:**\
Validates phone number formatting.

**Additional:**\
Optional `error` message.

***

## email

**Description:**\
Validates email format.

Pragmatic email validation based on: [https://www.regular-expressions.info/email.html](https://www.regular-expressions.info/email.html)

* Case-insensitive
* Prevents consecutive dots in domain
* Intentionally not RFC 5322 complete

For more restrictive needs please use [regex\_matches](#regex-matches) validator.

**Additional:**\
Optional `error` message.

***

## postal\_code

**Description:**\
Validates postal code format.

**Additional:**\
Optional `error` message.

***

## custom

**Description:**\
Custom validation function.

**Additional:**\
Requires a `key` and a `validateFn` that returns an error message if validation fails. The `validateFn` may be synchronous or asynchronous — it may return a `string | null | undefined` or a `Promise<string | null | undefined>`.

Example (async):

```ts theme={null}
{
  validate: 'custom',
  key: 'email_remote_check',
  validateFn: async (value) => {
    if (value && typeof value === 'string') {
      // simulate async check (e.g. remote service)
      const isEmailValid = await fetch('/api/validate-email', { method: 'POST', body: value });
      if(!isEmailValid) {
        return 'This email is too short';
      }
    }
    return undefined;
  },
}
```