What are runes?

rune /ro͞on/ noun

A letter or mark used as a mystical or magic symbol.

Runes are symbols that you use in .svelte and .svelte.js / .svelte.ts files to control the Svelte compiler. If you think of Svelte as a language, runes are part of the syntax — they are keywords.

Runes have a $ prefix and look like functions:

let let message: stringmessage = 
function $state<"hello">(initial: "hello"): "hello" (+1 overload)
namespace $state
Declares reactive state.
Example:
let count = $state(0);
https://svelte-5-preview.vercel.app/docs/runes#$state
@paraminitial The initial value$state('hello');

They differ from normal JavaScript functions in important ways, however:

• You don’t need to import them — they are part of the language
• They’re not values — you can’t assign them to a variable or pass them as arguments to a function
• Just like JavaScript keywords, they are only valid in certain positions (the compiler will help you if you put them in the wrong place)

Legacy mode

Runes didn’t exist prior to Svelte 5.