Why a live preview matters
Markdown’s whole promise is that the source is readable on its own — but the gap between what you type and what renders is exactly where mistakes hide. A table missing its separator row, a list that flattened because of inconsistent indentation, a link with a stray space — none of these are visible until something renders them. Writing with the rendered output beside you closes that loop instantly: you see the broken table the moment you type it, not after you publish.
The rules that catch everyone
A handful of CommonMark behaviors surprise newcomers because Markdown’s whitespace handling is deliberate, not accidental:
| You typed | You expected | What actually happens |
|---|---|---|
| One newline between lines | A line break | Lines join into one paragraph |
A table with no |---| row | A table | Renders as plain text |
* item with 1-space sublists | Nested list | Sublist flattens |
| Heading with no blank line before | A heading | Sometimes not parsed |
The fixes: end a line with two spaces (or a blank line) to force a break; always include the |---| separator under table headers; indent nested list items by 2–4 spaces consistently; and leave a blank line before block elements like tables and headings.
Markdown and HTML mix
CommonMark lets you drop raw HTML straight into Markdown, which is the escape hatch for anything Markdown can’t express — <details>/<summary> accordions, a styled <div>, an iframe embed. The preview renders both together. This is powerful, but it’s also why rendering untrusted Markdown is a security concern: any HTML (including <script>) passes through unless the renderer sanitizes it. For your own writing that’s a feature; for user-submitted Markdown, sanitize the output.
From preview to published HTML
When you’re happy with the render, the underlying HTML is clean and ready to paste into a web page, email template, or CMS. If you need the conversion as a repeatable step rather than a copy-paste — or you want to go the other direction, HTML back to Markdown — the dedicated Markdown to HTML converter handles both directions.