How to Highlight Text in Markdown

The ==highlight== syntax comes from extended Markdown dialects and was popularized by editors like Obsidian, Typora, and iA Writer. Parser libraries can usually opt in too: markdown-it has a mark plugin, remark has equivalents, and Pandoc enables ==text== through its mark extension. Wherever it is supported, the output is the HTML <mark> element, which browsers render with a yellow background by default. Like other emphasis markers, the equals signs must touch the text on both sides — == spaced out == stays literal even in processors that support the syntax. If you are unsure whether your renderer supports it, the failure mode is at least obvious: unsupported ==text== shows the equals signs in the output rather than silently mangling anything.

Where the double-equals syntax is unsupported but raw HTML passes through — many static site generators, documentation tools, and HTML-exporting pipelines — you can write the <mark> tag directly: <mark>highlighted phrase</mark>. This is also semantically the right element: <mark> means "relevant in the current context", the way a search tool highlights matched terms or a study guide marks passages, which is a different signal than the importance conveyed by <strong>. Because it is a real HTML element, you can restyle the highlight color with CSS wherever you control the stylesheet.

GitHub is the platform people ask about most, and the answer is simply no: GFM has no highlight extension, so ==text== renders with the equals signs visible. The conventional substitutes are **bold** when a few inline words need to stand out, `inline code` when the standout text is a token or value, and the alert callouts (> [!NOTE], > [!IMPORTANT], > [!WARNING]) when a whole block needs attention — alerts render as colored boxes with icons and are the closest visual relative of a highlighter pen on GitHub. Pick by scope: bold for a phrase, code for a value, an alert for a paragraph.

Because highlighting is non-standard, think about where your document will end up. Notes written in Obsidian with ==highlights== degrade to visible equals signs the moment they are pushed to a GitHub repo or run through a default-configuration site generator. If an Obsidian vault feeds a publishing pipeline, either enable a mark plugin in that pipeline or convert ==...== to <mark>...</mark> before publishing. Within Obsidian itself, highlights have a genuinely distinct role worth preserving: writers use bold for structural emphasis and highlights for reader-style annotation — "this is the passage that matters" — and collapsing the two into bold loses that distinction.