What Is Markdown? The Common Language of Text in the Age of AI and Obsidian

The word Markdown turns up more and more in articles about Obsidian, GitHub, and AI coding. It is the notation where you put “#” in front of a heading and “-” at the start of a bullet.

It looks like notation for developers, but I would argue it is worth knowing precisely if you use AI daily. The reason is that Markdown is a common language for text that is readable by humans and by AI alike.

Markdown adds structure while staying readable

On a web page, headings and links are expressed with HTML tags. Markdown lets you write that structure with far fewer symbols. The commonly used notation amounts to about this much:

# Heading

## Subheading

- A bullet
- Another item

**An important phrase**

[Link text](https://example.com/)

Looking at the unconverted text, you can still tell what is a heading and what is a list. Staying readable as-is was a particular priority in Markdown’s design.

Why it helps with AI, 1: structure travels with the text

When handing a long document to an AI, headings and bullets alone make the divisions in the information clear. Splitting purpose, constraints, and output format under Markdown headings makes it readable as a specification too.

Write a specification in Markdown and the same file a human reviewed can be read by Codex or Claude Code directly. There is no copying into a separate interface, and the diff after the AI rewrites something is easy to follow. For work that moves between prose and programs, that lightness pays off.

Why it helps with AI, 2: it is hard to lock inside an app

The contents of a Markdown file are, fundamentally, ordinary text. The extension is “.md”, but you do not need a particular app to open it. Notes written in Obsidian can be read in another editor, put on GitHub, and handed to an AI without friction.

That is also why I keep my second brain in Obsidian. Switch services and the text you have accumulated over years stays with you. Change AI and the same material can go to a different one.

Five pieces of notation are enough to start

• Headings: “#” at the start of a line
• Bullets: “-” at the start of a line
• Numbered lists: “1.”
• Emphasis: surround with “**”
• Links: square brackets followed by parentheses

Tables, checkboxes, and footnotes exist too, but there is no need to memorize them up front. When you need one, asking an AI to turn something into a Markdown checklist teaches you the notation along the way.

One caution: every app has its own dialect

Markdown has per-service extensions. Obsidian’s own note-to-note links, GitHub’s checkboxes — the same file can display differently in places. When moving files elsewhere, check whether any unusual notation is in them.

The basics, though — headings, bullets and the rest — are widely shared. As a foundation for holding on to your text long-term and moving it freely between apps and AI, Markdown is an unglamorous but very strong tool.

Reference: the official Markdown syntax. Features and specifications are as of July 2026.