# Add a custom linkifier

{!admin-only.md!}

Linkifiers make it easy to refer to issues or tickets in third
party issue trackers, like GitHub, Salesforce, Zendesk, and others.
For instance, you can add a linkifier that automatically turns `#2468`
into a link to `https://github.com/zulip/zulip/issues/2468`.

If the pattern appears in a message topic, Zulip adds a little button to the
right of the topic that links to the appropriate URL.

### Add a custom linkifier

{start_tabs}

{settings_tab|linkifier-settings}

1. Under **Add a new linkifier**, enter a **Pattern** and
**URL format string**.

1. Click **Add linkifier**.

{end_tabs}

## Understanding linkification patterns

This is best explained by example.

Hash followed by a number of any length.

* Pattern: `#(?P<id>[0-9]+)`
* URL format string: `https://github.com/zulip/zulip/issues/%(id)s`
* Original text: `#2468`
* Automatically links to: `https://github.com/zulip/zulip/issues/2468`

String of hexadecimal digits between 7 and 40 characters long.

* Pattern: `(?P<id>[0-9a-f]{7,40})`
* URL format string: `https://github.com/zulip/zulip/commit/%(id)s`
* Original text: `abdc123`
* Automatically links to: `https://github.com/zulip/zulip/commit/abcd123`

Generic GitHub `org/repo#ID` format:

* Pattern: `(?P<org>[a-zA-Z0-9_-]+)/(?P<repo>[a-zA-Z0-9_-]+)#(?P<id>[0-9]+)`
* URL format string: `https://github.com/%(org)s/%(repo)s/issues/%(id)s`
* Original text: `zulip/zulip#2468`
* Automatically links to: `https://github.com/zulip/zulip/issues/2468`

Linkifiers are implemented as a limited subset of Python 3 regular
expressions, with validation designed to prevent common mistakes,
avoid accidentally expensive linkifiers, and allow translation into
equivalent JavaScript regular expressions for local echo.

If you have any trouble setting these up, please [contact
us](/help/contact-support) with details on what you're trying to do,
and we'll be happy to help you out.