sveltejs/kit · error · Error

Invalid cache-control directive "${invalid}". Did you mean o

Error message

Invalid cache-control directive "${invalid}". Did you mean one of: ${[...VALID_CACHE_CONTROL_DIRECTIVES].join(', ')}? ${error_suffix}

What it means

Header validation applied to cache-control values set by the app: each comma-separated directive (the part before '=') is checked against the known cache-control directive set, and an unrecognized token triggers this error, including the offending token, the valid list, and a hint that it may be a typo.

Source

Thrown at packages/kit/src/runtime/server/validate-headers.js:35

	'min-fresh'
]);

const CONTENT_TYPE_PATTERN =
	/^(application|audio|example|font|haptics|image|message|model|multipart|text|video|x-[a-z]+)\/[-+.\w]+$/i;

/** @type {Record<string, (value: string) => void>} */
const HEADER_VALIDATORS = {
	'cache-control': (value) => {
		const error_suffix = `(While parsing "${value}".)`;
		const parts = value.split(',').map((part) => part.trim());
		if (parts.some((part) => !part)) {
			throw new Error(`\`cache-control\` header contains empty directives. ${error_suffix}`);
		}

		const directives = parts.map((part) => part.split('=')[0].toLowerCase());
		const invalid = directives.find((directive) => !VALID_CACHE_CONTROL_DIRECTIVES.has(directive));
		if (invalid) {
			throw new Error(
				`Invalid cache-control directive "${invalid}". Did you mean one of: ${[...VALID_CACHE_CONTROL_DIRECTIVES].join(', ')}? ${error_suffix}`
			);
		}
	},

	'content-type': (value) => {
		const type = value.split(';')[0].trim();
		const error_suffix = `(While parsing "${value}".)`;
		if (!CONTENT_TYPE_PATTERN.test(type)) {
			throw new Error(`Invalid content-type value "${type}". ${error_suffix}`);
		}
	}
};

/**
 * @param {Record<string, string>} headers
 */
export function validateHeaders(headers) {

View on GitHub (pinned to 03f1687fe6)

Solutions

Correct the directive name to one from the listed valid set (no-store, no-cache, must-revalidate, public, private, max-age, s-maxage, immutable, stale-while-revalidate, etc.)
Split custom/proprietary directives out — SvelteKit only validates cache-control; use another header name for non-standard policies
Check spelling case-insensitively: the validator lowercases, so 'Pulbic' still fails

Example fix

// before
event.setHeaders({ 'cache-control': 'pulbic, max-age=3600' });
// after
event.setHeaders({ 'cache-control': 'public, max-age=3600' });

Defensive patterns

Strategy: validation

Validate before calling

const VALID = new Set(['no-store','no-cache','must-revalidate','proxy-revalidate','must-understand','immutable','public','private','max-age','s-maxage','max-stale','min-fresh','stale-while-revalidate','stale-if-error','only-if-cached','no-transform']);
function validateCacheControl(value) {
  for (const part of value.split(',')) {
    const d = part.trim().split('=')[0].toLowerCase();
    if (!VALID.has(d)) throw new Error('Invalid cache-control directive: ' + d);
  }
}

Try / catch

try {
  event.setHeaders({ 'cache-control': cc });
} catch (e) {
  if (e.message.startsWith('Invalid cache-control directive')) console.error('Typo in directive:', cc);
}

Prevention

Keep a constant list of allowed directives in your codebase
Copy directive names from MDN rather than typing from memory
Note the validator lowercases input, so only spelling matters

When it happens

Trigger: setHeaders({ 'cache-control': 'max-age=60, pulbic' }) (typo for public); using non-standard directives like 'immutable ' misspelled or 'no-cache-store'; camelCase variants like 'Max-Age' are lowercased and fine, but wrong words are not.

Common situations: Hand-typed cache policies with typos; copying CDN-specific directives (e.g. s-maxage is valid, but 'stale-if-error' must be spelled exactly) that the validator doesn't recognize.

Related errors

AI-assisted analysis of sveltejs/kit@03f1687fe6 (2026-09-02). Data as JSON: /api/errors/98975faf07b17b30. Report an issue: GitHub.