Rich Text Editor
Formatting tools that don't let pasted HTML wreck your app.
What it adds
A WYSIWYG editor for long-form fields, with a fixed set of supported formats and server-side sanitisation of everything it produces.
What your agent is told to do
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What your agent is told to do
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Decide the supported format list first — headings, bold, italic, lists, links, quotes, code, images — and build the toolbar from it. An editor that accepts anything is an editor you cannot sanitise.
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Sanitise on the server against an allowlist of tags and attributes, both on save and on render. Client-side sanitisation is a convenience, not a defence; the endpoint accepts whatever is posted to it.
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Clean pasted content: strip inline styles, font tags, class names and comments from Word and Google Docs, and map what remains onto the supported formats.
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Keep the editable region a real focusable control with a label, and make every toolbar action reachable by keyboard with its shortcut shown.
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Do not store rendered HTML as the only copy if the app also needs plain text for search, previews or notifications — derive and store that too.
Edge cases it handles
6
Edge cases it handles
6- Content that looks empty but is a stray break or empty paragraph must count as empty for validation.
- Links must be checked for scheme — javascript: and data: URLs are the whole attack.
- Pasted images arrive as base64 or as remote URLs; decide whether to upload, rewrite or reject them, and never hotlink silently.
- Undo must survive a paste-and-clean operation as a single step, not unwind character by character.
- Autosave and formatting must not fight: a save mid-edit should not move the caret or reset the selection.
- Content authored before this editor existed must still open and save without being mangled.
Definition of done
8
Definition of done
8- Stored HTML is sanitised server-side against an explicit allowlist.
- Pasted Word and Docs content arrives clean and mapped to supported formats.
- Unsafe link schemes are rejected on save and on render.
- Every toolbar action has a keyboard path and headings produce real heading elements.
- Visually-empty content fails a required-field check.
- Legacy content round-trips through the editor unchanged.
- 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
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
Code Editor Field
Code Editor Field
Edit code, JSON, and config with syntax highlighting instead of a bare textarea.
What it does
A form field backed by a real code editor: syntax highlighting, a language mode per field, and inline validation that tolerates work in progress.
How it works
- 1 Load the editor library lazily, only on views that use it, and render a usable plain textarea until it arrives. It must never block first paint.
- 2 Set the language mode per field from what the field actually holds, and validate against that mode.
- 3 Report syntax errors as you go, but never block typing or reset the content. Half-written JSON is a normal intermediate state; only submission should be gated.
Copy the prompt
No account needed
Add this feature to my app:
https://addthisfeature.com/x/code-editor-field
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.