Slack Markdown and text formatting

Slack does not use Markdown. It uses mrkdwn, a smaller syntax that looks similar and disagrees in the places that matter most: *one asterisk* is bold, links use angle brackets, and there are no headings at all.

The differences, in one table

One asterisk, and why it bites

A single asterisk means italic in Markdown and bold in Slack. That is worse than an unsupported feature, because nothing visibly fails: paste a Markdown paragraph into Slack and *emphasis* arrives shouting. Text going the other way looks over-formatted in the same way.

Code blocks

Backticks work the same as in Markdown: one pair for inline code, three for a block:

```
one block of code
```

Two differences. Slack ignores the language hint, so ```js puts the letters js into the block rather than turning on highlighting: there is no syntax highlighting in a Slack message at all. And a block does not need to be on its own lines: three backticks anywhere in a message open one.

Everything inside is literal, which makes a code block the way to post text that must not format, including a Markdown snippet you want a colleague to read as source.

Tables in Slack

There is no table syntax in mrkdwn. Pipes and dashes render exactly as typed, so a Markdown table pasted into a message arrives as a wall of punctuation.

Four things people do instead, roughly in order of how well they work:

• A code block. Monospace keeps hand-aligned columns lined up, and it is the only method that survives being copied out again. Use the table generator to line the columns up, then paste the result inside triple backticks.
• A Canvas. Slack's document surface has real tables, with headers and sortable columns. This is the right answer for anything that will be read more than once.
• An attached file. A .md or CSV file renders with a preview and stays readable outside Slack.
• An image. Fast, and unreadable to anyone using a screen reader or searching for a value in it. Last resort.

The composer formats for you

By default Slack's message box is WYSIWYG: it applies formatting from the toolbar and its keyboard shortcuts rather than from characters you type, which is why typed mrkdwn often appears to do nothing. To type the syntax directly, turn on Format messages with markup in Preferences → Advanced.

Lists are part of that composer rather than part of mrkdwn: the bullet and number buttons, or Ctrl+Shift+8 and Ctrl+Shift+7. A typed hyphen stays a hyphen.

Getting a Markdown document into Slack

For anything longer than a paragraph, do not translate the syntax by hand. Open the document in the editor and use Export → Copy as rich text, then paste into Slack: the composer accepts formatted text and turns headings, lists and emphasis into its own formatting. Long documents are usually better as a Canvas or an attached .md file than as a message.

Where standard Markdown does apply

Slack's own developer surface uses the same mrkdwn in Block Kit's mrkdwn text objects, so bots and apps follow these rules too, not the Markdown rules. Canvases are the exception: they are a document editor with real headings and tables, closer to a wiki page than to a message.