Slack formatting: why bold uses one asterisk (full guide)

Slack looks like it speaks markdown, and that resemblance is exactly what gets people. Its formatting language is called mrkdwn, and it borrows the shape of markdown while quietly changing the most important rule: bold is a single asterisk, not two. Paste a polished ChatGPT message into a channel and half of it renders as raw symbols. This guide is the complete mrkdwn reference, starting with the asterisk gotcha and covering every style Slack actually supports.

The single-asterisk rule

In Slack, *bold* is bold. One asterisk on each side. Standard markdown, GitHub, Reddit, and ChatGPT all use **two**, and that mismatch is the number-one reason a Slack message comes out looking broken. When you paste text full of double asterisks, Slack does not bold anything. It reads the extra asterisk as a literal character and prints the stars around your word.

It is worth saying plainly because the fix is so small: delete one asterisk from each side. **important** becomes *important* and it bolds. Everything else in mrkdwn is close enough to markdown that this is the single rule most people need to unlearn.

The full Slack mrkdwn syntax

Here is every style Slack renders, with the exact characters to type:

• Bold — *text* (one asterisk, not two)
• Italic — _text_ (single underscores)
• Strikethrough — ~text~ (a single tilde)
• Inline code — `code` (single backticks)
• Code block — three backticks on their own line before and after the block
• Block quote — > quoted line at the start of a line
• Bulleted list — type - item and Slack renders it with a • bullet
• Numbered list — 1. item

Notice what is missing. There is no underline in Slack, and there are no markdown headings. If you paste an underlined heading from a document, the styling drops and you may be left with stray # characters. For emphasis, reach for bold or italic instead of trying to fake a heading. Links do not need masked syntax either. Paste a bare URL and Slack auto-links it, so you rarely need the angle-bracket link form by hand.

Bold, italic, and strikethrough

The three inline styles each use a single marker: one asterisk for bold, one underscore for italic, one tilde for strikethrough. You can stack them, so *_bold italic_* gives you both at once. This single-marker consistency is the mental model to keep. Where markdown doubles up its symbols, Slack halves them.

Strikethrough is a good example of the cross-app confusion this creates. It is one tilde in Slack, but two in Discord and Reddit. Copy a struck-through line from a Discord channel into Slack and the effect vanishes, because Slack sees a single tilde as the marker and the second tilde becomes part of your text.

Code, quotes, and lists

For anything with fixed spacing, wrap a few words in single backticks for `inline code`, or fence a longer block with three backticks on their own line above and below it. Code blocks are the most reliable way to paste a command, a snippet, or a table-like layout without Slack reflowing it.

Quotes use a leading > on a line. Lists behave the way you expect while rendering a little differently than you typed: you start each line with - , and Slack draws a proper bullet character for it. That is why a pasted list of dashes suddenly looks tidy in the channel. Lead a long message with a bold line, break the body into bullets, and drop anything spacing-sensitive into a code block, and even a wall of text reads cleanly.

Skip the memorizing

You do not have to keep these rules in your head. The Slack text formatter gives you a visual editor: paste your draft, style it with a toolbar, and Copy hands you clean mrkdwn with single-asterisk bold already converted. It also strips the invisible characters and markdown noise that make AI-written messages read as obviously automated, then re-emits exactly what Slack renders.

Formatting for other communities

Slack is only one dialect. If you cross-post the same update elsewhere, each destination flips the rules again. The Discord text formatter uses double-asterisk bold and adds spoilers and syntax-highlighted code blocks, and the Reddit text formatter speaks near-standard markdown with spoilers and tables of its own. For the full Discord reference, the Discord text formatting guide walks through every mark and the masked-link caveat. And if your real problem is a platform that deletes formatting on paste rather than mis-rendering it, the LinkedIn formatting guide covers that separate headache.

Learn the one-asterisk rule and Slack stops fighting you. Or let the formatter emit the mrkdwn and never count asterisks again.