# 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](/platform-overview/page-editor/page-editor-components/brick-configuration-panel.md), you'll set the **Sites** value to specify where a mod can run.

<figure><img src="/files/9xNUkd2a0aaGAAK8l7ug" 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/)


---

# Agent Instructions: Querying This Documentation

If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question.

Perform an HTTP GET request on the current page URL with the `ask` query parameter:

```
GET https://docs.pixiebrix.com/developing-mods/developer-concepts/types-of-mods/what-are-url-match-patterns.md?ask=<question>
```

The question should be specific, self-contained, and written in natural language.
The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.