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

# Tagging

You can supply extra context on errors and performance traces using tags.
Tags are key-value data that can be used to search and filter data.

<Warning>
  🔐 Do not send <strong>Personal Identifiable Information (PII)</strong> to AppSignal. Filter PII (e.g., names, emails) and use an ID, hash, or pseudonymized identifier instead. <br /> <br /> Use [Link Templates](https://docs.appsignal.com/application/link-templates) to link them back in your app.
</Warning>

<Note>
  📖 Also read our guides on how to set up [tags](/guides/tagging).
</Note>

## Tags

Tags can be used to add information that is not already part of the trace [metadata](/application/metadata) (request parameters, session data, request headers, etc.).

Using tags you can easily add more information to errors and performance issues tracked by AppSignal. Maybe while debugging an issue you want to know which user faced the problem, you can pass in the user id or maybe to easily access the user data you can pass in the URL of your admin panel (using link templates) which will take you directly to the customer page.

### Link templates

Tags can also be used to create link templates.
Read more about link templates in our [link templates guide](/application/link-templates).