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

# Check Username Availability

> Check whether a username is already taken in this project

Checks whether the specified username is already in use within the project. Returns a simple availability flag. Use this before prompting users to set a username to give instant feedback.

## Query Parameters

<ParamField query="username" type="string" required>
  The username to check. Lookup is exact-match against the stored (lowercased)
  value.
</ParamField>

## Response

On success, returns HTTP `200` with:

<ResponseField name="available" type="boolean">
  `true` if the username is not yet taken; `false` if it is already in use.
</ResponseField>

**Example — available:**

```json theme={null}
{ "available": true }
```

**Example — taken:**

```json theme={null}
{ "available": false }
```

## Error Responses

<AccordionGroup>
  <Accordion title="Invalid Query — 400">
    ```json theme={null}
    {
      "error": "...",
      "code": "username/invalid-query"
    }
    ```
  </Accordion>
</AccordionGroup>

## See Also

* [`useCheckUsernameAvailability` hook](/hooks/users/use-check-username-availability)