Slack Message Formatter

In short Slack uses mrkdwn, which is its own syntax and not Markdown, and converting between them needs more than a find and replace. Bold is a single asterisk where Markdown uses two. Italic is a single underscore. Strikethrough is a single tilde where Markdown uses two. Links are the biggest departure: Slack writes an angle-bracket form with the URL first and the label after a pipe, so a Markdown link has to be turned inside out rather than adjusted. Two things have no equivalent at all. Headings do not exist in mrkdwn, so a heading becomes a bold line on its own — which is what Slack's own composer does when you paste one. Bullet lists do not exist either, so the bullet becomes a literal character at the start of the line. Because those two are conversions rather than translations, the output matches what Slack itself produces rather than approximating it. The single-asterisk rule is the one that catches Markdown users, exactly as it does on WhatsApp, and for the same reason: both predate Markdown's dominance.