You just need to let codex use a Chrome extension to access your website, and then have it run a detailed benchmark to find the reasons for stuttering, slow loading, and so on.

After you have the causes, ask it for a remediation plan and start putting it into action.
In the end, your project will reach a front-end master’s performance level.
This is also the only loop operation with a positive ROI: use existing logs and analysis to find the problems, then fix them.