Having recently re-worked by personal blog, I recently stumbled upon Lighthouse. It is geared towards improving SEO, but really it is does a great job at helping create an optimized website in terms of performance, accessibility, and bugs.
From the plugin itself is an open-source, automated tool for improving the performance, quality, and correctness of your web apps.
When auditing a page, Lighthouse runs a barrage of tests against the page, and then generates a report on how well the page did. From here you can use the failing tests as indicators on what you can do to improve your app.
But even at 100%, there are always opportunities for improvements.