Markdown Editor with Preview
Write Markdown and see exactly how it will render.
What it adds
A source editor paired with a live preview, where the stored value stays raw Markdown and the rendered HTML is sanitised.
What your agent is told to do
5
What your agent is told to do
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1
Store the raw Markdown byte-for-byte. Never round-trip it through a rendered form and back — that silently rewrites people's spacing, list markers and escapes.
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2
Pick one Markdown flavour and one extension set, and use the same one on the client preview and the server renderer. A preview that disagrees with the published page is worse than no preview.
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Sanitise the generated HTML on the server before it is stored or served, including raw HTML blocks embedded in the source.
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Synchronise preview scroll to the editor loosely, anchored on block boundaries. Do not chase the caret.
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This is not a WYSIWYG surface. Toolbars that produce formatting directly and pasted-HTML cleanup are owned by Rich Text Editor; extend that rather than building a second editor here.
Edge cases it handles
6
Edge cases it handles
6- Fenced code blocks must render literally, including anything inside them that looks like Markdown or HTML.
- Raw HTML in the source must either be sanitised or disabled outright — decide and say which.
- Link and image URLs need scheme checks; a Markdown link is still a link.
- Scroll sync must not fight the user when they scroll the preview themselves.
- Very long documents must not re-render the whole preview on every keystroke — debounce it.
- Unsupported syntax must show as plain text, not silently vanish.
Definition of done
8
Definition of done
8- The stored value is the exact Markdown the user typed.
- Client preview and server render produce the same output for the same source.
- Generated HTML is sanitised server-side, including embedded raw HTML.
- Code fences render their contents literally.
- Scroll sync tracks the editor without jumping or hijacking manual preview scrolling.
- Preview rendering is debounced and stays responsive on long documents.
- 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
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
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
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.