# Snapchat URL Preview Service: User Agent and Blocking

> Snapchat fetches shared links with the Snap URL Preview Service to build chat previews. Its user agent, cache time, tags and how to block it.

The Snap URL Preview Service is the fetcher that Snapchat uses to build link previews in chat. It is not an AI crawler. If you want good previews in Snapchat, let it fetch your pages and add Open Graph tags. If you do not want previews, block its user agent on your server.

## What the service does

Snap describes the service on its [Snapchat Robots page](https://developers.snap.com/robots). When a Snapchat user shares a link with friends in chat, the service reads the HTML of that page. It then shows a card with a title, a subtitle and a thumbnail. The card links to the website.

The service reads Open Graph tags first, mainly `og:title` and `og:image`. If those tags are missing, it uses X/Twitter Card tags such as `twitter:title`. Snap says that it caches the response for each URL for 30 minutes. This limits repeated requests to the same URL.

The Snapchat Robots page lists only this one service.

## User-agent string

A user agent is the client name in the User-Agent HTTP header. Snap documents this user agent:

```text
Snap URL Preview Service; bot; snapchat; https://developers.snap.com/robots
```

## Fix missing previews

Snap gives two steps for links that do not display correctly:

1. Add the user agent above to the allow list of your website, firewall or bot protection.
2. Make sure that your pages return the metadata tags in the HTML head.

The guides to [Open Graph meta tags](/html-tags/open-graph-meta-tags/) and [Twitter Card meta tags](/html-tags/twitter-card-meta-tags/) explain the tags. Snap caches each URL for 30 minutes. So a new share during that time can still show the old tags.

## Block the service

robots.txt is a text file at the root of your site with rules for crawlers. Snap does not say whether the URL Preview Service reads robots.txt, and it names no robots.txt token. If you want to stop the requests, block the user agent on your web server. This nginx example returns HTTP 403 for any user agent that contains `Snap URL Preview Service`:

```nginx
if ($http_user_agent ~* "Snap URL Preview Service") {
    return 403;
}
```

Put the example in the `server` block of your site configuration, then reload nginx. Without access to your HTML, the service cannot build a preview card from your page.

## Verify requests

Snap publishes no IP list and no reverse DNS method for this service. Anyone can copy a user-agent string. A match in your logs does not prove that the request came from Snap.

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