Layout Shift Guard
Stop content jumping as a page loads, and catch it when it starts happening again.
What it adds
Reserved space for everything that arrives late, plus measurement that reports unexpected movement on the app's main screens.
What your agent is told to do
5
What your agent is told to do
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Walk the app's main screens with the network throttled and note everything that moves after first paint. Images, avatars, embeds, banners, ad slots, and asynchronously loaded panels are the usual sources.
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Give every image, video, iframe, and embed explicit dimensions or a fixed aspect ratio so its box exists before its content arrives, including the ones whose size comes from data.
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Control the swap from fallback to web font so the two have compatible metrics, and accept a slightly imperfect fallback over a page that reflows once the real font lands.
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Reserve space for anything conditional that appears above or beside existing content — validation messages, incident banners, trial notices, unsaved indicators — rather than letting it push the layout down when it arrives.
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Do not count movement the user asked for. Expanding a row, opening a drawer, or loading the next page on a click is intended motion, and a guard that flags it will be turned off within a week.
Edge cases it handles
7
Edge cases it handles
7- Media and embeds without declared dimensions collapse to nothing and then snap to full size; every one needs a reserved box, including those sized from record data.
- A fallback font with different metrics to the real one reflows every paragraph when the swap happens, so the two must be matched or the swap must be suppressed until the real font is ready.
- Banners, toasts, and validation messages are the most common late arrivals in an app that has otherwise been optimised, and each needs its space held open in advance.
- Movement caused directly by a user action must be excluded from measurement, or the signal is drowned in noise and stops being actionable.
- Sticky headers and action bars that change height on scroll will register as shifts unless their reserved height is fixed; this overlaps Sticky Action Bar, which owns the pinning behaviour while this entry owns the space reservation.
- A skeleton placeholder must match the real content's dimensions. A skeleton that is the wrong height causes the shift it was meant to prevent.
- Measurement must run on the devices and connections real users have, not only on a fast machine where everything arrives before first paint.
Definition of done
8
Definition of done
8- Every image, video, iframe, and embed on the main screens has reserved dimensions before its content loads.
- Font swapping produces no visible reflow of surrounding text.
- Conditional banners and validation messages appear in space already held for them.
- Layout movement is measured on the app's main screens and reported.
- Movement resulting from a direct user action is excluded from the measurement.
- Skeleton placeholders match the dimensions of the content that replaces them.
- The feature matches the existing design system.
- No existing functionality is broken.
Related features
Visual Asset Optimization Pipeline
Visual Asset Optimization Pipeline
Turn source artwork into small, correct derivatives without losing the detail that matters.
What it does
A repeatable processing step that derives sized and compressed variants for every image, icon, and illustration the app ships.
How it works
- 1 Locate every visual asset the app serves — bundled artwork, icons, illustrations, and user uploads — and bring them all through one processing path instead of optimising some by hand.
- 2 Keep the untouched original of every asset in a place the pipeline can reach, so a change in format or quality target can be applied by reprocessing rather than by re-sourcing artwork nobody can find.
- 3 Set the compression target per kind of asset. A photograph tolerates aggressive compression; a screenshot containing text and a flat illustration with hard edges show artefacts at the same setting.
Copy the prompt
No account needed
Add this feature to my app:
https://addthisfeature.com/x/visual-asset-optimization-pipeline
Bundle-Aware Component Imports
Bundle-Aware Component Imports
Stop a single icon or helper from dragging a whole library into the shipped bundle.
What it does
Import rules and a check that keep component and icon libraries from arriving whole when only a fraction is used.
How it works
- 1 Inspect what the app currently ships and identify the packages whose contribution is far larger than the number of things imported from them. Icon sets, chart libraries, and date utilities are where this usually starts.
- 2 Import from the narrowest entry point each package offers, and where a package cannot be reduced, wrap it behind a local module so the constraint is enforced in one place instead of at every call site.
- 3 Audit the app's own shared index files. A single index re-exporting every component means importing one thing can reach everything, including modules with side effects that defeat elimination entirely.
Copy the prompt
No account needed
Add this feature to my app:
https://addthisfeature.com/x/bundle-aware-component-imports
Adaptive Media Source Component
Adaptive Media Source Component
Serve each image and video at a size and format the viewer's device can actually use.
What it does
One media component that chooses source, format, and dimensions from the rendered box and the browser's declared support.
How it works
- 1 Find every place the app renders a raw image or video element and route them all through a single component, so source selection is decided in one place rather than per template.
- 2 Derive the candidate widths from the sizes the element is genuinely rendered at across the app's breakpoints, and describe those sizes to the browser accurately — an inaccurate size hint is worse than none.
- 3 Always render an intrinsic width and height or an aspect ratio, so the box occupies its final space before any bytes arrive.
Copy the prompt
No account needed
Add this feature to my app:
https://addthisfeature.com/x/adaptive-media-source-component
How it works
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1
Copy the link
Grab the Markdown instruction URL for this feature.
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2
Give it to your AI
Paste it into Claude Code, Cursor, v0, Lovable — whatever you build with.
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It inspects, then implements
Your agent reads your existing app first, then adds the feature to fit it.
Works with your stack
These instructions are written to adapt. They tell the agent to detect your framework, match your existing design system, and reuse what you already have — rather than assuming a particular stack.
Need it tighter than that? Customize the feature and tell it exactly what you're running.