Class Merge Helper
Combine conditional classes in one place so the last one written actually wins.
What it adds
A single helper every component uses to resolve base, conditional, and caller-supplied classes into one final list.
What your agent is told to do
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What your agent is told to do
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Find every component that currently builds a class string by hand and route all of them through one helper, so the resolution rules are identical everywhere.
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Define the precedence plainly: the component's own base classes lose to its variant classes, and both lose to whatever the caller passed in. A caller that supplies a class expects it to take effect.
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Accept the shapes calling code actually produces rather than forcing every call site to normalise first, and make the behaviour for absent and empty values explicit rather than incidental.
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Detect and collapse conflicting utilities that set the same property, keeping the last one, so a caller adjusting one aspect of a component does not have to fight a base class that is still present.
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Do not let this helper decide policy. Which utilities are permitted and when a pattern should be extracted belong to Utility Class Conventions; this helper only resolves what it is given.
Edge cases it handles
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Edge cases it handles
6- A caller passing a class to change one property must win over the component's own class for that property. If the base class survives, the override silently does nothing and the caller will reach for importance flags instead.
- Values arriving as lists, as objects keyed by condition, and as absent or empty entries must all be handled without special-casing at the call site, and must never contribute stray separators or empty entries to the output.
- Conflicts between classes belonging to different systems — a utility framework class against a hand-written or component class targeting the same property — cannot be resolved by name matching alone. Define the resolution rule and state its limits.
- An invalid or misspelled class name must survive to the output unchanged rather than being quietly dropped, because a helper that swallows typos turns a visible styling bug into an invisible one.
- The helper runs on every render of every component, so its cost is multiplied by the size of the tree and must stay proportionate to the classes it is given.
- Ordering must be stable: the same inputs must produce the same output string every time, or server-rendered and client-rendered markup will disagree.
Definition of done
8
Definition of done
8- Every component composes classes through the single helper, with no hand-built class strings remaining.
- Caller-supplied classes reliably override the component's own classes for the same property.
- Lists, condition maps, and absent values are all accepted and produce no empty or duplicated entries.
- Conflicting utilities setting the same property collapse to the last one given.
- Unrecognised class names pass through unchanged.
- The same inputs always produce the same output string.
- The feature matches the existing design system.
- No existing functionality is broken.
Related features
Variant Class Generator
Variant Class Generator
Declare a component's variants once instead of scattering conditionals through its markup.
What it does
A declarative variant definition per component mapping size, tone, and state to the classes each combination produces.
How it works
- 1 Find the components whose markup is threaded with conditional class logic and replace that logic with a single declaration listing each variant, its options, and its default.
- 2 Support combinations that are more than the sum of their parts, so a specific pairing of size and tone can produce classes that neither produces alone, without reintroducing a conditional in the markup.
- 3 Make invalid combinations impossible to express rather than merely undesirable, and give the component a defined appearance when it receives a combination it does not recognise.
Copy the prompt
No account needed
Add this feature to my app:
https://addthisfeature.com/x/variant-class-generator
Tokenized Inline Styles
Tokenized Inline Styles
Allow styles computed at runtime without letting arbitrary values escape the design system.
What it does
A constrained path for dynamically computed styles, where every value is either a design token or a number clamped to an approved range.
How it works
- 1 Find every place the app already sets a style value at runtime — progress widths, chart bar heights, avatar colours, drag positions, user-chosen accent colours — and sort them into two groups: values that must come from the token set, and values that are genuinely continuous numbers.
- 2 For the first group, accept only token names and resolve them to values at the boundary. A caller passing a raw colour or a raw pixel value should be rejected loudly in development rather than quietly rendered.
- 3 For the second group, clamp to a documented minimum and maximum and round to a sensible precision, so a percentage of 4000 or a width of 0.3847291 pixels never reaches the DOM.
Copy the prompt
No account needed
Add this feature to my app:
https://addthisfeature.com/x/tokenized-inline-styles
CSS Custom Property Bridge
CSS Custom Property Bridge
Expose the design tokens as CSS variables so theming and styling can change at runtime.
What it does
A generated layer of CSS custom properties mirroring the token source, which components are expected to style against.
How it works
- 1 Generate the custom properties from the same token source the rest of the app already uses, so a token and its variable can never disagree. A hand-maintained parallel list will drift within a release.
- 2 Decide and document where each group of variables is declared — the document root for global theme values, a container for anything that must vary per section or per component — and apply that rule consistently.
- 3 Fix the naming scheme and treat the generated names as a public contract, since stylesheets, components, and any customer-facing theming all reference them by name.
Copy the prompt
No account needed
Add this feature to my app:
https://addthisfeature.com/x/css-custom-property-bridge
How it works
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1
Copy the link
Grab the Markdown instruction URL for this feature.
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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.