How to Convert Markdown to HTML Instantly
Markdown is a plain-text shorthand that maps onto a small set of HTML tags. You write a hash for a heading and asterisks for emphasis, and a converter produces the markup. The Markdown to HTML Converter does it in your browser.
What maps cleanly
The core is stable everywhere. Hashes become heading tags, with the number of hashes setting the level. Paired asterisks or underscores become emphasis and strong emphasis. A blank line separates paragraphs. Hyphens or numbers at the start of a line become lists. Square brackets followed by parentheses become a link, and the same with a leading exclamation mark becomes an image. Backticks become code, and indented or fenced blocks become preformatted code.
That set covers the overwhelming majority of what anyone writes, and it behaves identically in every converter.
Where the flavours disagree
Beyond the core, Markdown is not one language. Tables, task lists, strikethrough, footnotes, automatic linking of bare URLs and fenced code with a language label are all extensions, present in some converters and absent from others.
So a document that renders beautifully in one place can come out as literal asterisks and pipe characters in another. If a document has to work in more than one system, stay inside the core. The practical test is to run it through the target system early rather than discovering the gap at publication.
Line breaks are the subtlest difference. A single newline inside a paragraph is ignored by the original specification and treated as a break by several popular flavours, which is why text that looked right in a notes app arrives as one long run-on paragraph elsewhere.
The security point
Most converters pass raw HTML straight through, because Markdown was designed to allow it. That is fine for your own writing and dangerous for anyone else's: if you convert text a visitor submitted and put the result on a page, they can include a script tag and it will run.
Converting untrusted Markdown means sanitising the output afterwards, or using a converter that escapes HTML instead of passing it. Escaping the input first with the HTML Entity Encoder also works, at the cost of making genuine HTML impossible.
Common questions
Can I convert HTML back to Markdown?
Partly. Simple markup round-trips; tables, nested structures and anything with attributes or inline styles do not survive.
Why do my tables not render?
Tables are an extension rather than core Markdown, so a converter that does not implement them shows the pipe characters literally.
Does the converter upload my text?
No. It runs in your browser, which matters for a draft you have not published.
Why did my single line breaks disappear?
The original specification treats them as spaces. Leave a blank line for a new paragraph, or check whether your target system implements the line-break extension.
Is Markdown good for a long document?
For prose, yes. For anything needing precise layout, footnoting or cross-references, it will fight you.
Got Markdown to turn into markup?