sveltejs/kit · error · Error

No matcher found for parameter '${names.values().next().valu

Error message

No matcher found for parameter '${names.values().next().value}'

What it means

When routes use param matchers, SvelteKit needs the params module that defines them. `load_and_validate_params` collects all matcher names used across routes and throws this error when the `params_path` option is absent even though at least one route needs a matcher. It reports the first missing matcher name to point the developer at the configuration gap.

Source

Thrown at packages/kit/src/utils/params.js:50

	}
}

/**
 * @param {{
 *   routes: import('types').RouteData[];
 *   params_path: string | null;
 *   root: string;
 *   load?: (file: string) => Promise<Record<string, unknown>>;
 * }} opts
 * @returns {Promise<Record<string, ParamMatcher> | null>}
 */
export async function load_and_validate_params({ routes, params_path, root, load }) {
	const names = collect_matcher_names(routes);

	if (names.size === 0) return null;

	if (!params_path) {
		throw new Error(`No matcher found for parameter '${names.values().next().value}'`);
	}

	const file = path.resolve(root, params_path);
	const module = load ? await load(file) : await import(pathToFileURL(file).href);

	if (!module.params || typeof module.params !== 'object') {
		throw new Error(`${params_path} does not export \`params\` from \`defineParams\``);
	}

	validate_param_matchers(
		/** @type {Record<string, unknown>} */ (module.params),
		names,
		params_path
	);

	return /** @type {Record<string, ParamMatcher>} */ (module.params);
}

View on GitHub (pinned to 03f1687fe6)

Solutions

Configure `params_path` in the relevant API call (e.g. `load_and_validate_params`/manifest options) to point at the module exporting `defineParams` params
Create the params module and export the matcher referenced by the reported parameter name
Remove the matcher usage (e.g. `[slug]` instead of `[slug=slug]`) if matchers are not needed

Example fix

// before
const manifest = await load_and_validate_params({ routes, root, load });
// after
const manifest = await load_and_validate_params({
	routes,
	root,
	params_path: 'src/params.js',
	load
});

Defensive patterns

Strategy: validation

Validate before calling

if (routes.some((r) => /\[\w+=/.test(r.id)) && !paramsPath) {
	throw new Error('Routes use matchers but params_path is not configured');
}

Try / catch

try {
	await load_and_validate_params(opts);
} catch (e) {
	if (e.message.startsWith('No matcher found')) {
		// configure params_path before retrying
	}
	throw e;
}

Prevention

Always set params_path in programmatic/adapter usage when routes may contain matchers
After migrating from src/params/*.js files, verify the new single-module config is wired up
Lint route folder names to detect `=matcher` usage early

When it happens

Trigger: `load_and_validate_params` is invoked (e.g. during manifest updates or param resolution) with `params_path` null/undefined while `collect_matcher_names(routes)` returned at least one matcher name.

Common situations: Using dynamic routes with matchers without configuring the params file path; upgrading SvelteKit where params moved from `src/params/*.js` files to a single `defineParams` module and the config was not updated; programmatic API use where `params_path` was omitted.

Related errors

AI-assisted analysis of sveltejs/kit@03f1687fe6 (2026-09-02). Data as JSON: /api/errors/59936cc849c32d19. Report an issue: GitHub.