Most slow sites were fast when they launched. Sort of. They launched without a speed review, and the problems were invisible until someone ran PageSpeed Insights three months later and saw a score in the 30s.
A pre-launch speed checklist prevents that. It takes 30-60 minutes to run through, catches the issues that compound into major performance problems, and means you never have to send an apologetic email about site speed to a client two weeks after launch.
Here is the exact checklist I run on every site before it goes live.
Images
This is the biggest single category of pre-launch speed wins. And the most commonly skipped.
Check every above-the-fold image. Confirm it is resized to display dimensions (not the original 4000-pixel source), compressed to WebP at 75-80% quality, and set to load eagerly (not lazy). The hero image is almost always the LCP element. If it is oversized or lazy-loaded, LCP will be poor from day one.
Check every below-the-fold image. Confirm they are lazy-loaded. Every image below the initial viewport should have loading="lazy" so the browser does not download them until the user scrolls.
Check for decorative images that should be CSS. Gradient overlays, simple shapes, and background textures often do not need to be images at all. A CSS gradient loads in zero time. A 200 KB PNG adds weight every page load.
Video
Check for autoplay background video. If the hero has an autoplay video, confirm it is under 2 MB for a short loop, or replaced with a poster image that loads the video after the page is interactive. A 10 MB autoplay video tanks LCP on every page load.
Check for YouTube or Vimeo embeds. Embedded video players load their own JavaScript, CSS, and preview images on page load even if the user never clicks play. Use a facade: show a thumbnail image with a play button, and only load the iframe when the user clicks.
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Count loaded font weights. Open the page source or network tab and count how many font files download. If you see more than 3 (regular, bold, and maybe one more), you are loading weights that are probably not used. Remove them.
Check for font-display: swap. Confirm that your font loading CSS or Google Fonts URL includes font-display: swap so text is visible immediately while custom fonts load.
Check for font preloading. The primary body font weight should have a <link rel="preload"> in the head to start downloading early.
Scripts
Audit every third-party script. Open the network tab and filter by JS. List every script that loads. For each one, ask: does this need to load on initial page render? Analytics, chat widgets, heatmaps, and marketing pixels can almost always be deferred or lazy-loaded.
Check GTM tag count. If using Google Tag Manager, open the container and count the tags. If there are more than 15-20, review each one. Dead tags, duplicate tags, and overly broad triggers are common. Each unnecessary tag adds main thread work and hurts INP.
Check for render-blocking scripts. Any script in the head without defer or async blocks rendering. Move non-critical scripts to defer loading or to the end of the body.
Core Web Vitals
Run PageSpeed Insights on the top 5 pages. Test the homepage, a key service/product page, a blog post, a listing page, and the contact page. These represent the most common page templates.
Check LCP element on each page. The diagnostics section identifies the LCP element. Confirm it is not lazy-loaded, is properly sized, and loads as a priority resource.
Check CLS on each page. Look for layout shift warnings. Common pre-launch CLS sources: images without dimensions, ads or embeds without reserved space, and fonts swapping with large metric differences.
Check INP on interactive pages. Pages with forms, toggles, filters, and modals need INP testing. Use the Web Vitals Chrome extension and interact with every element. Target under 200ms.
Mobile
Test on a real mid-tier device. Your development MacBook Pro is not representative. Use Chrome DevTools device emulation at minimum, but a real device test is better. A Moto G Power or Samsung Galaxy A-series gives you realistic performance data.
Check mobile-specific issues. Hamburger menus that load heavy JavaScript. Image carousels that are touch-laggy. Forms that are hard to fill on mobile. These are user experience problems that also affect performance metrics.
Check mobile image sizes. If responsive images are set up, confirm that mobile devices receive smaller image files, not the desktop version scaled down in CSS.
Hosting and CDN
Verify CDN configuration. Confirm the CDN is active and serving assets from edge locations near your audience. A misconfigured CDN serves everything from the origin server, adding hundreds of milliseconds of latency.
Check caching headers. Static assets (images, fonts, CSS, JS) should have long cache durations (at least 30 days). HTML pages should have shorter caching or revalidation headers.
Test from the target audience's location. If your audience is primarily in one region, test from that region. Use tools like WebPageTest or GTmetrix to run tests from specific server locations.
The report
After running through the checklist, I generate a before-and-after comparison for the client:
- PageSpeed scores for each tested page
- LCP, INP, and CLS values from lab data
- Issues found and fixes applied
- Remaining recommendations that require client input (removing scripts, changing content)
This report becomes the baseline for post-launch monitoring. When field data starts arriving in 28 days, I compare it against the lab baseline to confirm the optimizations are holding in production.
Why this matters for your launch
Running a structured speed review before launch means:
- No awkward performance conversations with your team or users later
- Higher Search Console scores from day one
- A documented baseline that demonstrates the quality of the build
- Fewer post-launch support requests for "why is the site slow"
It takes less than an hour and it saves weeks of remediation work. If you want to build this kind of rigor into your process, or if you are an agency utilizing my white-label design and development services to ship fast builds to your clients, that is exactly what my strategy work delivers.