markdown-to-slack-mrkdwn

Convert standard Markdown to Slack mrkdwn format.

Why?

Slack uses its own markup syntax (mrkdwn) that differs from standard Markdown. This converter handles the tricky edge cases that simpler converters miss:

• Tables — converted to aligned, preformatted code blocks
• Bold/italic conflicts — **bold** and *italic* coexist without breaking
• Code blocks — protected from formatting, language specifiers removed
• Inline code — preserved inside text, stripped inside tables
• Links & images — [text](url) becomes <url|text>
• Lists — - and * become bullet points
• Headings — # Title becomes *Title* (bold)
• Strikethrough — ~~text~~ becomes ~text~
• Horizontal rules — --- becomes ———

Zero dependencies. Works with Node.js 18+.

Install

npm install markdown-to-slack-mrkdwn

Usage

As a module (ESM)

import { markdownToSlack } from 'markdown-to-slack-mrkdwn';

const slack = markdownToSlack('# Hello **world**');
// → '*Hello world*'

As a CLI

echo "# Hello **world**" | npx markdown-to-slack-mrkdwn
# → *Hello world*

Or install globally:

npm install -g markdown-to-slack-mrkdwn
echo "**bold** and *italic*" | md-to-slack
# → *bold* and _italic_

Use --split to get a JSON array of chunks safe for Slack's message limit:

cat report.md | md-to-slack --split
# → ["chunk1...", "chunk2...", ...]

TypeScript

Types are included out of the box:

import { markdownToSlack, splitForSlack } from 'markdown-to-slack-mrkdwn';
// markdownToSlack(text: string): string
// splitForSlack(text: string, options?: { maxLength?: number }): string[]

Splitting long messages

Slack truncates messages over ~4000 characters, which can break code blocks mid-table. Use splitForSlack to split the output into safe chunks:

import { markdownToSlack, splitForSlack } from 'markdown-to-slack-mrkdwn';

const mrkdwn = markdownToSlack(longMarkdown);
const messages = splitForSlack(mrkdwn); // default: 3500 chars per chunk

for (const msg of messages) {
  await slack.chat.postMessage({ channel, text: msg });
}

Custom limit:

const messages = splitForSlack(mrkdwn, { maxLength: 2000 });

Code blocks are never split — each chunk has properly paired ``` markers.

Examples

| Markdown | Slack mrkdwn | |----------|-------------| | **bold** | *bold* | | *italic* | _italic_ | | ~~strike~~ | ~strike~ | | [link](url) | <url\|link> | | # Heading | *Heading* | | - item | \u2022 item | | `code` | `code` | | --- | \u2014\u2014\u2014 |

Markdown tables are converted to aligned preformatted blocks:

| Name  | Score |        ```
|-------|-------|  →     Name    Score
| Alice | 95    |        Alice   95
| Bob   | 87    |        Bob     87
                         ```

License

MIT