Describe a time you had to improve the performance of a slow page. What did you do?

Tell it as measurement first, guessing never.

• What the complaint was, and what the data said. These often differ. Real user monitoring beats a lab test on your own laptop, because your laptop is not the user's phone.
• Which metric was actually bad. Naming the specific Core Web Vital shows you know they have different causes: LCP is usually images or a slow server response, CLS is missing dimensions or late-injected content, INP is long JavaScript tasks blocking the main thread.
• How you profiled. The Performance panel for main-thread work, the Network waterfall for request chains, the Coverage tab for unused CSS and JavaScript.
• What you changed. Typical high-value fixes: code splitting a route, lazy-loading below-the-fold images, adding width and height attributes, replacing a heavy dependency, preloading a font, or moving work off the main thread.
• The before and after numbers, and any business metric that moved with them.

Note: Mention the budget or CI check you added afterwards so the improvement did not silently erode.