sveltejs/kit · error · Error

${directory}: `__pathname` is a reserved query parameter for

Error message

${directory}: `__pathname` is a reserved query parameter for `isr.allowQuery`

What it means

For ISR routes, adapter-vercel uses the synthetic `__pathname` query parameter internally to map a request URL to its prerendered variant. Users may not reserve it in `isr.allowQuery`, since allowing it would corrupt the cache-key mapping, so the adapter throws during adapt().

Source

Thrown at packages/adapter-vercel/index.js:123

					throw new Error('The `edge` runtime is no longer supported');
				}

				const runtime = resolve_runtime(defaults.runtime, route.config.runtime);

				const config = { ...defaults, ...route.config, runtime };

				if (is_prerendered(route)) {
					if (config.isr) {
						ignored_isr.add(route.id);
					}
					continue;
				}

				if (config.isr) {
					const directory = path.relative('.', builder.config.files.routes + route.id);

					if (config.isr.allowQuery?.includes('__pathname')) {
						throw new Error(
							`${directory}: \`__pathname\` is a reserved query parameter for \`isr.allowQuery\``
						);
					}

					isr_config.set(route, {
						expiration: config.isr.expiration,
						bypassToken: config.isr.bypassToken,
						allowQuery: ['__pathname', ...(config.isr.allowQuery ?? [])],
						group: isr_config.size + 1,
						passQuery: true
					});
				}

				const hash = hash_config(config);

				// first, check there are no routes with incompatible configs that will be merged
				const pattern = route.pattern.toString();
				const existing = conflicts.get(pattern);

View on GitHub (pinned to 03f1687fe6)

Solutions

1. Remove '__pathname' from the route's isr.allowQuery array
2. List only real user-facing query parameters in allowQuery
3. Rebuild after the config change

Example fix

// before
export const config = { isr: { expiration: 60, allowQuery: ['__pathname', 'lang'] } };
// after
export const config = { isr: { expiration: 60, allowQuery: ['lang'] } };

const allowQuery = config?.isr?.allowQuery ?? [];
if (allowQuery.includes('__pathname')) {
  throw new Error('isr.allowQuery must not include the reserved "__pathname" param');
}

const reservesPathname = (config) =>
  Array.isArray(config?.isr?.allowQuery) && config.isr.allowQuery.includes('__pathname');

try {
  await build();
} catch (err) {
  if (err.message.includes('__pathname')) {
    console.error('Remove __pathname from isr.allowQuery in the named route config.');
  }
  throw err;
}

When it happens

Trigger: A route's config sets `isr: { allowQuery: ['__pathname', ...] }` (or includes '__pathname' anywhere in the allowQuery array).

Common situations: Developer lists every query param the route can receive, inadvertently including __pathname after seeing it in generated Vercel config or URLs; cargo-culting from another project's ISR config.

Related errors

• Invalid isr.expiration value: ${JSON.stringify(value)} (${de
• The `edge` runtime is no longer supported
• The ${route.id} and ${existing.route_id} routes must be merg
• Warning: The following routes have an ISR config which is i
• The _headers file should be placed in the project root rathe

AI-assisted analysis of sveltejs/kit@03f1687fe6 (2026-09-02). Data as JSON: /api/errors/cc5f1ba9aefaa8b5. Report an issue: GitHub.