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
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What your agent is told to do
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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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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
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
Input Group Component
Input Group Component
Join prefixes, suffixes, and buttons to an input so they read as one control.
What it does
A composite control binding an input to adjoining affixes and buttons within a single visual frame.
How it works
- 1 Find the places the app already fakes this — a currency symbol floating beside a number field, a copy button jammed next to a token, a domain suffix drawn as separate text — and rebuild them as one group.
- 2 Draw the focus treatment around the whole group when any child inside it holds focus, so the composite reads as one control rather than a box beside a button.
- 3 Give the group one accessible name from the field's label and describe affixes separately; a currency symbol or a unit must be exposed as description, not as a second label.
Copy the prompt
No account needed
Add this feature to my app:
https://addthisfeature.com/x/input-group-component
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.