Fix Cumulative Layout Shift (CLS) — Bolt

Q: How do I set dimensions on responsive images?

Use `width` and `height` attributes with the raw dimensions, plus CSS `height: auto`. Browser calculates aspect ratio and reserves space.

Q: font-display: swap or optional?

`swap` is standard but can cause CLS. `optional` prevents shift but may not load the custom font on slow connections. Test both.

CLS happens when content jumps during load — you click something and hit the wrong element. Google penalizes it; users hate it.

rocket_launch

Fixing this in Bolt

StackBlitz in-browser AI app builder with WebContainers

Bolt projects run inside a browser container — file paths are real, but the deploy target varies. Paste the prompt below into your Bolt chat and the fix rolls out across the project in one pass.

Using a different tool? Pick your stack:

Lovable Cursor Bolt v0 Replit Windsurf Claude Code Base44

The prompt for Bolt

Copy and paste this into your Bolt chat exactly as-is.

In Bolt, please update my project with these exact changes:

Fix Cumulative Layout Shift

1. Add explicit width and height to all images and video elements.
2. Avoid inserting content above existing content dynamically.
3. Use font-display: swap for web fonts.

Why this matters

CLS is the "janky load" metric. When images load without declared dimensions, the page height jumps — and users often click the wrong button mid-shift.

Core Web Vital — Google rewards CLS < 0.1 and penalizes > 0.25. Easy fix: explicit dimensions everywhere.

How to use this prompt in Bolt

1. Open your Bolt project.
2. Copy the prompt above with the copy button.
3. Paste into the Bolt chat and send.
4. Review the diff, accept the changes, redeploy.
5. Verify the fix using the checklist below.

Common mistakes to avoid

error_outlineImages without width/height — the #1 cause of CLS.
error_outlineLate-loading web fonts that swap and shift text.
error_outlineInjecting banner/cookie notices above existing content.
error_outlineAdding ads or embeds without reserved space.

How to verify the fix worked

check_circlePageSpeed Insights → CLS < 0.1.
check_circleDevTools Performance → Experience → Layout Shift events — none over 0.05.
check_circleRecord a slow mobile load (4G throttle) — no visible jumps.

Frequently asked questions

How do I set dimensions on responsive images?expand_more

Use `width` and `height` attributes with the raw dimensions, plus CSS `height: auto`. Browser calculates aspect ratio and reserves space.

font-display: swap or optional?expand_more

`swap` is standard but can cause CLS. `optional` prevents shift but may not load the custom font on slow connections. Test both.

Want all 34 prompts tailored to your Bolt site?

Pantra scans your site in 10 seconds, detects the stack, and generates the exact prompts that apply — only the ones you actually need.

Scan my site

Related Bolt prompts

Performance