Unit Converter
Let people convert a value between units without leaving the page they are on.
What it adds
An inline converter that takes a typed value in one unit and shows the equivalent in another, in place.
What your agent is told to do
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What your agent is told to do
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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.
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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.
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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.
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Hold the canonical value in a single base unit internally and convert out to whatever is displayed, so switching units repeatedly does not accumulate error.
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Do not implement conversion as a flat table of pairwise multipliers. It grows quadratically, and the pairs nobody thought to add will silently return nothing.
Edge cases it handles
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Edge cases it handles
8- Converting a value out and back must return the value the user typed. Rounding the display separately from the stored value produces drift that shows up as 1 becoming 0.99999 after three switches.
- People type decimals with a comma as well as a period depending on their locale. Accept both on input, and do not treat a comma as a thousands separator in a field that expects a single number.
- Do not report more significant figures than the input justifies. Two inches converted to millimetres is not 50.800000 mm, and showing it that way implies a precision the user never gave.
- Temperature and some pressure scales have an offset as well as a ratio. A converter that only multiplies will get Celsius to Fahrenheit wrong for every value except zero.
- A request to convert between incompatible dimensions, such as kilograms to metres, must be refused with a clear message rather than producing a number. Only offer units in the same dimension in the target selector.
- Empty, partial, and non-numeric input must show nothing rather than an error or a zero. A user mid-keystroke has not made a mistake yet.
- Very large and very small magnitudes must stay readable. Decide whether to switch to exponential notation or to a larger unit, and apply the rule consistently.
- The converted value must be announced to screen readers when it changes, not only rendered visually next to the field.
Definition of done
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Definition of done
9- A value converted to another unit and back matches the original exactly.
- Both comma and period decimal separators are accepted on input.
- Displayed precision reflects the precision of the input rather than the float behind it.
- Offset scales such as temperature convert correctly across their whole range, including negatives.
- Only units in the same dimension are offered, and incompatible conversions are refused with an explanation.
- Numbers render through the app's existing formatting rather than a second implementation.
- Result changes are announced accessibly.
- The feature matches the existing design system.
- No existing functionality is broken.
Related features
Help Text Pattern
Help Text Pattern
Put field guidance in one predictable place, phrased the same way every time.
What it does
A consistent treatment for the short explanatory text that sits with a field and its control.
How it works
- 1 Collect the guidance the app currently scatters across placeholders, tooltips, asterisked footnotes, and modal help, and move it into one slot beneath the field.
- 2 Keep guidance that is required to complete the field permanently visible. A format rule hidden behind a hover target is not available to a touch user or a keyboard user.
- 3 Write help as the rule the user needs before typing — the accepted format, the consequence of the choice — not as a restatement of the label.
Copy the prompt
No account needed
Add this feature to my app:
https://addthisfeature.com/x/help-text-pattern
Voice Dictation
Voice Dictation
Put a microphone in text fields so people can speak their input instead of typing it.
What it does
A dictation control on the app's longer text inputs that transcribes speech into the field as the user talks.
How it works
- 1 Add the control to the fields where typing is genuinely tedious: long descriptions, notes, comments, and message bodies. A microphone on a postcode field is clutter.
- 2 Show interim results in the field as they arrive, visually distinct from committed text, so the speaker can see it is working and correct course before they finish.
- 3 Reuse the app's existing Voice Transcription for the server-side path so one recognition configuration and one set of language settings serve both dictation and recorded audio.
Copy the prompt
No account needed
Add this feature to my app:
https://addthisfeature.com/x/voice-dictation
Form Section Pattern
Form Section Pattern
Break long forms into labelled sections people can scan instead of read.
What it does
A section pattern grouping related fields under a heading, a description, and its own actions.
How it works
- 1 Find the forms that have grown past a screenful — settings, profiles, checkout, configuration — and group their fields by the question each group answers, not by the table the columns come from.
- 2 Give each section a heading in the document's heading order and an optional one-line description, so screen reader and keyboard users can jump between sections.
- 3 Allow at most one level of nesting. A section inside a section inside a tab gives the user no orientation and pushes the fields into a narrow gutter.
Copy the prompt
No account needed
Add this feature to my app:
https://addthisfeature.com/x/form-section-pattern
How it works
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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.