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

# Custom functions

> Give an agent a custom tool it can call during a call - per phone number.

Add a custom function (tool) to a phone number so the AI can call your own HTTPS endpoint during a call and use the result. Configured **per phone number**.

## Add a custom function

<ParamField path="phoneNumber" type="string" required>
  The phone number in E.164 format, passed in the URL.
</ParamField>

<ParamField body="name" type="string" required>
  Tool name in `snake_case` (lowercase letters, numbers, underscores), max 64 characters.
</ParamField>

<ParamField body="url" type="string" required>
  Your HTTPS endpoint the AI will call. `https` only.
</ParamField>

```bash theme={null}
curl -X POST "https://api.nixflex.com/v1/integrations/custom-functions/number/+447446466847" \
  -H "Authorization: Bearer nxf_xxx:nxfs_xxx" \
  -H "Content-Type: application/json" \
  -d '{"name": "check_order_status", "url": "https://your-app.com/order-status"}'
```

## List custom functions

```bash theme={null}
curl -X GET "https://api.nixflex.com/v1/integrations/custom-functions/number/+447446466847" \
  -H "Authorization: Bearer nxf_xxx:nxfs_xxx"
```

## Remove a custom function

Delete a specific function by its `id`:

```bash theme={null}
curl -X DELETE "https://api.nixflex.com/v1/integrations/custom-functions/number/+447446466847/FUNCTION_ID" \
  -H "Authorization: Bearer nxf_xxx:nxfs_xxx"
```

## Notes

* The number must belong to your account. A number you do not own returns `404`.
* For how custom functions work in a call, see [Custom functions](/advanced/custom-functions).