sveltejs/kit · error

Cookie "${name}" is too large, and will be discarded by the

Error message

Cookie "${name}" is too large, and will be discarded by the browser

What it means

Dev-only size check in the internal cookie setter: the encoded name+value pair exceeds SvelteKit's MAX_COOKIE_SIZE (4096 bytes, the browser cookie limit). In development SvelteKit throws so the problem is caught early; in production browsers would silently drop the cookie, losing session data.

Source

Thrown at packages/kit/src/runtime/server/cookie.js:253

		let path = options.path ?? '/';

		if (!options.domain || options.domain === url.hostname) {
			path = resolve(normalized_url, path);
		}

		// Generate unique key for cookie storage
		const cookie_key = generate_cookie_key(options.domain, path, name);
		const cookie = { name, value, options: { ...options, path } };
		new_cookies.set(cookie_key, cookie);

		if (DEV) {
			const size =
				// only the name/value pair counts towards MAX_COOKIE_SIZE, not the other attributes
				text_encoder.encode(name).byteLength +
				text_encoder.encode((options.encode ?? encodeURIComponent)(value)).byteLength;

			if (size > MAX_COOKIE_SIZE) {
				throw new Error(`Cookie "${name}" is too large, and will be discarded by the browser`);
			}

			cookie_paths[name] ??= new Set();

			if (!value) {
				cookie_paths[name].delete(path);
			} else {
				cookie_paths[name].add(path);
			}
		}
	}

	/**
	 * @param {import('types').TrailingSlash} trailing_slash
	 */
	function set_trailing_slash(trailing_slash) {
		normalized_url = normalize_path(url.pathname, trailing_slash);
		internal_queue.forEach((fn) => fn());

View on GitHub (pinned to 03f1687fe6)

Solutions

1. Store large data server-side (e.g. in a database or session store) and keep only a session id in the cookie
2. Shorten the cookie value or use a less verbose encoding

When it happens

Trigger: Thrown at packages/kit/src/runtime/server/cookie.js:253 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of sveltejs/kit@03f1687fe6 (2026-09-02). Data as JSON: /api/errors/009ecf0facf39514. Report an issue: GitHub.