To prevent the router from matching on invalid input, you can specify a matcher. For example, you might want a route like /colors/[value] to match hex values like /colors/ff3e00 but not named colors like /colors/octarine or any other arbitrary input.

First, create a new file called src/params/hex.js and export a match function from it:

export function match(value) {
	return /^[0-9a-f]{6}$/.test(value);
}

Then, to use the new matcher, rename src/routes/colors/[color] to src/routes/colors/[color=hex].

Now, whenever someone navigates to that route, SvelteKit will verify that color is a valid hex value. If not, SvelteKit will try to match other routes, before eventually returning a 404.

Matchers run both on the server and in the browser.