SlowFinder

SlowFinder measures where your site spends its time during a front-end request and attributes that time to the plugin (or theme, or WordPress core) responsible for it.

During a profiled request the plugin wraps every registered hook callback in a lightweight timer, records each callback’s “self” time (excluding time spent inside other callbacks it triggers) and the database queries it ran, then maps the callback back to the plugin that defined it using PHP Reflection. Results are averaged across samples and shown as a ranked table with bars.

Two ways to run it

• Automatic — the site makes background (loopback) requests to the page for you. Fastest, fully hands-off.
• Manual — the plugin sets a short-lived cookie in your browser and you open the page yourself. Because it profiles a genuine visit from your real browser, it works even when Cloudflare bot fighting mode, “Under Attack” mode, or a hardened host blocks automated loopback requests. No server-to-server request is made.

More info: https://slowfinder.com