Markdown flavors compared: CommonMark, GFM, Discord, Slack, Obsidian, Notion, Reddit, Jira, MDX, Pandoc, reStructuredText

What is the difference between CommonMark and GFM?

CommonMark is the unambiguous base specification of markdown: headings, emphasis, lists, links, images, code, blockquotes, raw HTML. GitHub Flavored Markdown is a strict superset that adds five extensions — tables, task lists, strikethrough, bare-URL autolinks and an HTML tag filter — and github.com adds alerts, footnotes, math, mermaid, emoji shortcodes and references on top. Anything valid in CommonMark renders the same in GFM.

GFM cheat sheet with the GFM vs CommonMark table →

Which markdown flavor should I write in?

GFM, unless you are targeting one specific app. It is the default of GitHub, GitLab, VS Code preview, most static site generators, remark/markdown-it, Obsidian's shared subset and every AI assistant's output. For chat apps (Slack, Discord, Telegram, WhatsApp) write in their dialect at send time rather than pasting GFM.

Is Slack markdown?

No. Slack calls its format mrkdwn and documents it as "inspired by markdown, but uses different rules": *single asterisks* are bold, _underscores_ italic, ~tildes~ strikethrough, links are <url|text>, and there are no headings, tables, images or list syntax. Pasting GFM into Slack produces visible asterisks and brackets.

Slack formatting sheet →

What is the difference between reStructuredText and Markdown?

Both are plain-text markup, but reST is a single formal spec (docutils) with an extensible directive system (.. note::, .. image::, .. toctree::) and roles (:math:`x`), while markdown is a family of dialects with raw HTML as the escape hatch. reST uses ``double backticks`` for code, `text <url>`_ for links and underlined titles; it has no bold-italic, no task lists and no pipe tables. Sphinx and Python documentation use reST; almost everything else uses markdown. Pandoc converts between them.

Why does my markdown look different on Discord, Slack, Notion and Reddit?

Because each one implements its own parser with its own rules. Discord treats __ as underline and has no tables or images; Slack uses single-character markers and ignores [text](url); Notion converts > into a toggle while typing and has only three heading levels; Reddit adds >!spoilers!< and ^superscript and, on old Reddit, lacks fenced code. The matrix above shows the exact syntax per element so you can rewrite before pasting.

What is the most portable markdown?

The CommonMark core written in its most common form: **bold**, *italic*, # headings up to H3, - bullets, 1. numbers, [text](https://url), ```fenced code, > quotes with every line prefixed, blank lines between blocks, and pipe tables when you need them. Skip HTML, shortcodes, alerts, footnotes and anything with a platform name in this matrix. The portability table lists the swaps.

Are MDX and Pandoc markdown separate flavors?

Yes, in opposite directions. MDX is markdown (CommonMark + GFM via plugins) that also parses JSX, import/export and {expressions}; it drops indented code, autolinks and raw HTML in exchange. Pandoc's markdown is the broadest superset — fenced divs, bracketed spans, four table styles, citations, definition and example lists, inline footnotes, ^super^ and ~sub~ — meant for converting to LaTeX, DOCX and HTML rather than for rendering in an app.

Pandoc markdown sheet →