Notify404 is a utility tool that allows you to keep tabs on broken links. The principle is simple: when MODX serves a Page not Found error, you get an email with all the details you need to fix the link or to setup a redirect. It can also alert you of (failed) hack attempts, and as of 1.2.0 (which is currently being tested) it works together with the Rampart package (as of version 1.3.1) to completely ban users snooping around for exploits from your site.
You can use Notify404 for free and you can install it via the MODX Revolution Package Manager. It is available for download as a transport package on MODX.com, and you can get the source from Github. Github is also the place for bugs and feature requests and I'll gladly review and accept pull requests for added or improved functionality.
Future improvements I'm hoping to incorporate as time allows:
- Ability to add configurable filters / ban matches to prevent getting swamped with emails.
- Ability to send daily/weekly/monthly digests instead of an email as the 404 happens.
- Back-end component to review 404's that occured.