> For the complete documentation index, see [llms.txt](https://docs.transparentedge.eu/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.transparentedge.eu/security/block-by-ua.md).

# Blocking User-Agent

Blocking a User-Agent is straightforward. You just need to add these lines to your configuration file within the vcl\_recv function and customize it according to your needs.

```javascript
sub vcl_recv{
    if (req.http.User-Agent ~ "^curl") { 
        call deny_request;
    } 
}
```

In this example, any request with a User-Agent starting with the word curl will be denied with a 403 Forbidden response. The 403 response is triggered by calling `deny_request` which blocks the requests immediately**.**


---

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