Mathematics

Mathematics is rendered with KaTeX, which implements a large, fast subset of LaTeX math mode. If you write LaTeX, you already write this.

Inline math

Wrap in single dollars:

The map $f: X \to Y$ is continuous if $f^{-1}(U)$ is open for every open $U$.

The map $f : X \to Y$ is continuous if $f^{- 1} (U)$ is open for every open $U$ .

The LaTeX delimiters $ ... $ work too, so sources pasted from a .tex file render without rewriting.

Wrap in double dollars on their own lines:

$$
\int_{-\infty}^{\infty} e^{-x^2} \, dx = \sqrt{\pi}
$$

\int_{- \infty}^{\infty} e^{- x^{2}} d x = π

\[ ... \] is equivalent. Display math that overflows a narrow screen scrolls horizontally instead of breaking the layout.

The standard alignment environments work inside display math:

$$
\begin{aligned}
(a+b)^2 &= a^2 + 2ab + b^2 \\
(a-b)^2 &= a^2 - 2ab + b^2
\end{aligned}
$$

(a + b)^{2} (a - b)^{2} = a^{2} + 2 ab + b^{2} = a^{2} - 2 ab + b^{2}

Also available: cases, matrix / pmatrix / bmatrix / vmatrix, gathered, array. See the full list of supported environments.

You write	You get
`\frac{a}{b}`, `\tfrac{a}{b}`	$\frac{a}{b}$ , $\frac{a}{b}$
`\sqrt{x}`, `\sqrt[3]{x}`	$x$ , $3 x$
`x_i`, `x^2`, `x_i^2`	$x_{i}$ , $x^{2}$ , $x_{i}^{2}$
`\sum_{i=1}^{n}`	$\sum_{i = 1}^{n}$
`\int_a^b`, `\oint`	$\int_{a}^{b}$ , $\oint$
`\lim_{x \to 0}`	$lim_{x \to 0}$
`\alpha, \beta, \Gamma, \Omega`	$α, β, Γ, Ω$
`\mathbb{R}, \mathcal{L}, \mathfrak{g}`	$R, L, g$
`\leq, \geq, \neq, \approx, \equiv`	$\leq, \geq, \neq =, \approx, \equiv$
`\in, \subset, \cup, \cap, \setminus`	$\in, \subset, \cup, \cap, ∖$
`\to, \mapsto, \implies, \iff`	$\to, \mapsto, ⟹, ⟺$
`\infty, \partial, \nabla, \hbar`	$\infty, \partial, \nabla, ℏ$
`\langle x, y \rangle`	$⟨ x, y ⟩$
`\hat{x}, \bar{x}, \vec{v}, \dot{x}`	$\overset{x}{^}, \overset{x}{ˉ}, v, \overset{x}{˙}$

The authoritative reference is KaTeX's supported functions page.

Errors render in place. A command KaTeX does not know renders the raw source in red rather than failing the page – you see exactly what to fix.
Math mode only. KaTeX renders math, not LaTeX documents: no \documentclass, no \section, no text-mode environments. Document structure is Markdown's job; only the mathematics goes in dollars.
No custom macros. \newcommand definitions do not persist across math spans; write commands out in full.
A literal dollar sign is \$ in prose. Inside code spans and code blocks, $ is always literal and math is never rendered.
Diagrams (commutative diagrams, tikzcd) are not math-mode KaTeX – use a TikZ block.