Mismatched route config for ${route.id} — the +page and +ser

Error message

Mismatched route config for ${route.id} — the +page and +server files must export the same config, if any

What it means

When a route has both +page and +server files, SvelteKit requires any page-level `export const config` and endpoint-level `export const config` to match exactly. JSON-unequal configs for the same key cause this error, because one route cannot carry two different configurations.

Source

Thrown at packages/kit/src/core/postbuild/analyse.js:108

	// analyse routes
	for (const route of manifest.routes) {
		const page =
			route.page &&
			analyse_page(
				route.page.layouts.map((n) => (n === undefined ? n : nodes[n])),
				nodes[route.page.leaf]
			);

		const endpoint = route.endpoint && analyse_endpoint(route, await route.endpoint());

		if (page?.prerender && endpoint?.prerender) {
			throw new Error(`Cannot prerender a route with both +page and +server files (${route.id})`);
		}

		if (page?.config && endpoint?.config) {
			for (const key in { ...page.config, ...endpoint.config }) {
				if (JSON.stringify(page.config[key]) !== JSON.stringify(endpoint.config[key])) {
					throw new Error(
						`Mismatched route config for ${route.id} — the +page and +server files must export the same config, if any`
					);
				}
			}
		}

		const route_config = page?.config ?? endpoint?.config ?? {};
		const prerender = page?.prerender ?? endpoint?.prerender;

		if (prerender !== true) {
			for (const feature of list_features(
				route,
				manifest_data,
				server_manifest,
				tracked_features
			)) {
				check_feature(route.id, route_config, feature, config.adapter);
			}

View on GitHub (pinned to 03f1687fe6)

Solutions

Make the `config` exports in +page.js and +server.js identical (deep-equal) for that route.
Or remove `config` from one of the files if it's only meaningful for one side's deployment.
If the page and endpoint truly need different configs, split them into different route directories.

Example fix

// before (+server.js)
export const config = { runtime: 'experimental_node' };
// after (match +page.js)
export const config = { runtime: 'nodejs20' };

Defensive patterns

Strategy: validation

Validate before calling

const pageConfig = (await import('./src/routes/demo/+page.js')).config;
const serverConfig = (await import('./src/routes/demo/+server.js')).config;
if (pageConfig && serverConfig &&
    JSON.stringify(pageConfig) !== JSON.stringify(serverConfig)) {
  throw new Error('+page and +server config exports must be identical');
}

Try / catch

try {
  await build();
} catch (e) {
  if (String(e.message).includes('Mismatched route config')) {
    console.error('Sync the `config` exports between +page.js and +server.js in:', e.message);
  } else throw e;
}

Prevention

Keep a single shared constant (e.g. export const config from a common module) imported by both files.
After editing adapter-specific config, update both +page and +server in mixed routes.
Review git diffs of one side for a route directory to catch the other side needing the same change.

When it happens

Trigger: A route directory with +page.js exporting `config = { runtime: 'edge' }` and +server.js exporting a different `config` (different values, or one side missing a key the other has, when both define config).

Common situations: Adapter-specific configs (e.g. Cloudflare/Vercel runtime) diverging between +page and +server during iterative edits; one teammate updating page config but not the server config.

Related errors

AI-assisted analysis of sveltejs/kit@03f1687fe6 (2026-09-02). Data as JSON: /api/errors/1d857b33eb2c8c2c. Report an issue: GitHub.