# What Are URL Match Patterns?

PixieBrix uses URL match patterns to determine whether or not a mod should run on a web page. For each mod, you can define the URL match patterns using a combination of any of the following:

* **Wildcards.** Use wildcards to match any character or sequence of characters.
* **Regular expressions.** Use regular expressions to allow for more advanced filtering.
* **Fixed text strings.** Use \*\*\*\*fixed string matches for exact matches.

### Important Things to Know

* If PixieBrix does not have access to a site, you will be prompted to grant access.
* URL match pattern rules are optional, but if you add them, ensure that at least one URL matches the patterns you add.

### Setting URL Match Patterns

You'll see the URL match pattern in the Starter Brick for each mod. The Starter Brick is the first brick in a mod, and must be one of the following: 

* Trigger
* Sidebar
* Context Menu
* Quick Bar
* Button

In the Starter Brick [Configuration Panel](https://docs.pixiebrix.com/platform-overview/page-editor/page-editor-components/brick-configuration-panel), you'll set the **Sites** value to specify where a mod can run.

<figure><img src="https://2274778196-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2Fq123bF1HPQPV35s5vHa1%2Fuploads%2FClv5xmu9WOf50XirJo4d%2Fimage.png?alt=media&#x26;token=ebf2cd60-ec18-45c1-9eba-c07e1ba12769" alt=""><figcaption></figcaption></figure>

### Related Topics

* [Mozilla URL Pattern API](https://developer.mozilla.org/en-US/docs/Web/API/URL_Pattern_API)
* [Chrome Developer Match patterns](https://developer.chrome.com/docs/extensions/mv2/match_patterns/)