Product Variant Picker
Let shoppers pick size and colour and see price, image, and stock update as they choose.
What it adds
An option selector on the product page that resolves the chosen combination to a specific variant and updates price, imagery, and availability live.
What your agent is told to do
5
What your agent is told to do
5-
1
Model options as named groups with ordered values, and map each valid combination to a concrete variant with its own price, stock level, and identifier. The picker resolves a selection to a variant; it does not guess.
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Update price, availability, and the main image the moment a selection changes, without a page reload and without resetting the other groups the shopper has already chosen.
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Reflect the selected variant in the URL so a shared or refreshed page opens on the same choice. Read that value on load and apply it before first paint so the page does not visibly switch options.
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4
Drive the product's imagery through the existing Product Image Gallery rather than swapping a lone image element. When a variant has its own photos, the gallery switches to them; when it does not, it stays on the product's default set.
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5
Do not let an invalid combination be submitted and rejected at add-to-cart. Compute which values are still reachable given the current selection and disable the rest, with a reason on the disabled value.
Edge cases it handles
8
Edge cases it handles
8- Combinations that do not exist must be visibly unavailable in the picker, not discovered when add-to-cart fails. Recompute reachable values on every change, and when a shopper's earlier choice becomes impossible, tell them which one you cleared.
- The chosen variant belongs in the URL so it survives sharing, refresh, and the back button. Use the same identifier the server understands, and fall back to the default variant if the value is stale or unknown.
- Variants can differ in more than price. Weight, shipping class, and tax treatment all change the total, so the picker must surface a changed delivery cost rather than letting it appear as a surprise at checkout.
- A variant with no image of its own must fall back to the product's default imagery rather than rendering a broken or empty frame.
- Option groups must be keyboard navigable with arrow keys and announced as a named group with a current selection. Colour swatches need a text label as well as the colour; colour alone is not a label.
- A product with a single variant should not show a picker at all, and a product with hundreds of combinations needs the groups presented as selects rather than a grid of swatches.
- Price and stock must be re-checked server-side when the item is added. The picker's view of availability is a convenience, not authority.
- Selecting an out-of-stock but real combination should still be allowed if the app offers back-in-stock notification, so the shopper can register interest rather than hit a dead end.
Definition of done
8
Definition of done
8- Choosing options updates price, availability, and imagery without a page reload.
- Combinations that do not exist are disabled with a reason, and add-to-cart never fails on an invalid selection.
- The selected variant is encoded in the URL and restored on load before first paint.
- Variants without their own images fall back to the product default with no broken frame.
- Option groups are operable by keyboard and announced with their current selection.
- Variant-specific price, weight, and shipping differences are reflected before checkout.
- The feature matches the existing design system.
- No existing functionality is broken.
Related features
Unit Converter
Unit Converter
Let people convert a value between units without leaving the page they are on.
What it does
An inline converter that takes a typed value in one unit and shows the equivalent in another, in place.
How it works
- 1 Start from the units the app actually deals in. A shipping tool needs weight and length; a recipe tool needs volume and temperature. Ship those and leave the rest out.
- 2 Convert as the user types, with the result visible beside the input rather than behind a submit button. Let either side be edited so the conversion runs in both directions.
- 3 Reuse the app's existing number parsing and display formatting rather than writing new ones. If Locale-Aware Numbers and Dates or Number Formatting Component is already present, the converter must render through it so grouping and decimal marks match the rest of the app.
Copy the prompt
No account needed
Add this feature to my app:
https://addthisfeature.com/x/unit-converter
Field State Matrix
Field State Matrix
Decide once how every field looks and behaves in every state, before screens improvise.
What it does
A defined and documented set of visual and behavioural states covering every input type in the app.
How it works
- 1 Enumerate the app's input types and cross them against every state they can enter: empty, filled, focused, hovered, invalid, valid, disabled, read-only, loading, and browser-autofilled.
- 2 Define disabled and read-only as genuinely different states — a read-only field shows a real value the user may select and copy, a disabled field is inert and excluded from submission.
- 3 Define the loading state so the field is visibly busy and not editable, and say what happens to a keystroke that arrives mid-load rather than letting it be silently swallowed.
Copy the prompt
No account needed
Add this feature to my app:
https://addthisfeature.com/x/field-state-matrix
Required Field Indicator
Required Field Indicator
Make it obvious which fields must be filled in and which may be left alone.
What it does
A consistent marking of required and optional fields across every form in the app.
How it works
- 1 Count the required and optional fields across the app's forms and pick the convention that marks the minority — if most fields are required, mark the optional ones instead.
- 2 Apply the chosen convention to every form without exception, and state the convention once at the top of each form so the marker means something to a first-time reader.
- 3 Expose the requirement to assistive technology as well as visually, so the control itself reports that it is required rather than relying on a symbol beside the label.
Copy the prompt
No account needed
Add this feature to my app:
https://addthisfeature.com/x/required-field-indicator
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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3
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.