Files and directories prefixed with + are reserved (saw ${pr

Error message

Files and directories prefixed with + are reserved (saw ${project_relative})

What it means

This is the final fallback in analyze(): any `+`-prefixed file or directory in src/routes that is neither a recognized Svelte component nor a recognized JS/TS module is rejected. SvelteKit reserves the entire `+` namespace under routes, so a +node_modules dir, +assets folder, or +README.md will abort sync with this message.

Source

Thrown at packages/kit/src/core/sync/create_manifest_data/index.js:573

		if (!match) {
			throw new Error(`Files prefixed with + are reserved (saw ${project_relative})`);
		} else if (match[3] || match[6]) {
			throw new Error(
				// prettier-ignore
				`Only Svelte files can reference named layouts. Remove '${match[3] || match[6]}' from ${file} (at ${project_relative})`
			);
		}

		const kind = match[1] || match[4] || match[7] ? 'server' : 'universal';

		return {
			kind,
			is_page: !!match[2],
			is_layout: !!match[5]
		};
	}

	throw new Error(`Files and directories prefixed with + are reserved (saw ${project_relative})`);
}

/**
 * @param {string} needle
 * @param {string} haystack
 */
function count_occurrences(needle, haystack) {
	let count = 0;
	for (let i = 0; i < haystack.length; i += 1) {
		if (haystack[i] === needle) count += 1;
	}
	return count;
}

View on GitHub (pinned to 03f1687fe6)

Solutions

Rename the file/directory so it does not start with `+`, or move it out of src/routes.
Use the documented reserved names only (+page, +layout, +error, +server with allowed extensions).
Store shared code outside src/routes (e.g. src/lib) rather than prefixing with `+`.

Example fix

// before
src/routes/+components/Button.svelte
// after
src/lib/components/Button.svelte

Defensive patterns

Strategy: validation

Validate before calling

for (const entry of fs.readdirSync('src/routes', { recursive: true })) {
  if (path.basename(String(entry)).startsWith('+') && !/^\+(page|layout|error|server)(\..+)?$/.test(path.basename(String(entry)))) {
    throw new Error(`Reserved + prefix on non-route entry: ${entry}`);
  }
}

Type guard

function isReservedRouteEntry(basename) {
  return basename.startsWith('+');
}

Try / catch

null

Prevention

Never name files or folders with a leading + anywhere under src/routes.
Keep backups, notes, and helpers in src/lib or outside the routes tree.
Add a pre-commit check that flags + prefixed unknown entries in routes.

When it happens

Trigger: A `+`-prefixed path in src/routes that matches no component or module pattern: directories like +components/, files like +notes.md, +data.json, or +helpers.js (unrecognized base name).

Common situations: Folders starting with + such as +stash/ or +backups/ inside routes; dependency output accidentally written into src/routes with a + prefix; users inventing files like +store.js expecting special behavior.

Related errors

AI-assisted analysis of sveltejs/kit@03f1687fe6 (2026-09-02). Data as JSON: /api/errors/929ffd471504a72f. Report an issue: GitHub.