One to six # characters, then a space, then the text. The number of hashes is the level, not the size: # is the document title, ## a major section, ### a subsection. Do not skip levels for visual effect — screen readers and table-of-contents generators read the structure, and most renderers build anchor links from it.

Use exactly one # per document. Everything below it steps down. Two details matter: the space after the hashes is required in strict parsers, and a heading needs a blank line before it if a paragraph sits directly above.

A paragraph is one or more lines of text with a blank line above and below. Markdown ignores single newlines inside a paragraph and joins the lines together, which surprises almost everyone the first time — an address or a poem collapses into one run-on line.

There are three fixes. A blank line makes a new paragraph, which is usually what you want. Two trailing spaces at the end of a line force a break inside the same paragraph; they are invisible, so many editors strip them. A backslash at the end of the line does the same thing and is visible in the source, which is why it is the safer habit.

One asterisk either side for italic, two for bold, three for both, two tildes for strikethrough. Underscores work for italic and bold too, but asterisks are safer: snake_case_variables contain underscores, and some parsers italicise part of the word.

The markers must hug the text. **bold** works; ** bold ** renders the asterisks literally, because a space after the opening marker cancels it. To show a literal asterisk, put a backslash in front of it.

Bullets start with -, * or + followed by a space. Pick one and stay with it; switching markers mid-list starts a second list in most parsers. Numbered lists start with 1., and the numbers you type after that are ignored, so a list written 1. 1. 1. still renders 1, 2, 3. That is handy when you insert a step in the middle.

Nest by indenting the child items, two spaces for bullets. Use spaces, never tabs: a tab is often read as a code block instead. Checklists and the rest of the detail are in the lists guide.

A link is the text in square brackets followed by the address in round brackets, with no space between the two brackets — that space is the single most common reason a link renders as literal text. An image is the same thing with an exclamation mark in front, and the bracketed text becomes the alt text rather than a visible label.

Bare URLs become clickable on their own in most renderers, including this one. If a URL contains spaces, replace each with %20 or the link breaks at the first space.

Wrap inline code in single backticks so a command keeps its own font and no character inside it is treated as formatting. For a block, put three backticks on their own line above and below, and write the language name after the opening fence to get syntax highlighting wherever the renderer supports it.

Block quotes start each line with a >. Add a second > to nest a quote inside a quote, and keep the > on the blank line between paragraphs so they stay in the same quote.

Tables are not in the original Markdown; they come from GitHub Flavored Markdown and work in nearly every modern renderer, this one included. A table is a header row, a divider row of dashes, then the body rows, with pipes between the cells.

The pipes do not need to line up — the columns are decided by the divider row, not by whitespace. Colons in that row set alignment: on the left for left, both ends for centre, the right for right. A table needs a blank line above it if text comes first. More, including how to escape a pipe, in the tables guide.

Every rule above, in one file, the way a real README looks. Three things worth noticing: blank lines separate every block, the table's pipes are not aligned and it renders correctly anyway, and the whole document is still readable as plain text — which is the point of the format.

The core — headings, emphasis, lists, links, images, quotes, code — behaves the same everywhere. Beyond that, expect differences.

Slack and Discord support bold, italic, strikethrough and code but not headings, tables or inline [text](url) links. Obsidian adds [[wiki links]] and callouts. Notion accepts Markdown as you type but stores its own blocks. GitHub adds footnotes and > [!NOTE] alerts; this viewer supports neither of those, nor raw HTML, which is disabled so a pasted document can never inject markup into the page. When it matters, test the document where it will actually be read, and keep the cheat sheet open.