In the past week I've written a broken-link checker, in perl, to sanity-check the output of a static-site-generator.

I've also written a trivial PHP parser which was designed to match up class-definitions with comments above them:

https://blog.steve.fi/parsing_php_for_fun_and_profit.html

Both of these tools were designed to be invoked by CI/CD systems, to flag potential problems before they became live.

Most of my work involves scripting, or tooling, around existing systems and solutions. For example another developer-automation hack was to automatically add the `approved` label to pull-requests which had received successful reviews from all selected reviewers - on a self-hosted Github Enterprise installation.