sveltejs/kit · error · Error

${keypath} should be true or false, if specified

Error message

${keypath} should be true or false, if specified

What it means

The `boolean` validator throws when a boolean config option receives a non-boolean value. Flags like `kit.prerender.crawl`, `kit.prerender.enabled`, or `handleHttpErrors`-style toggles must be literal true/false — truthy strings such as 'true' are rejected.

Source

Thrown at packages/kit/src/core/config/options.js:469

 * @returns {Validator}
 */
function number(fallback) {
	return validate(fallback, (input, keypath) => {
		if (typeof input !== 'number') {
			throw new Error(`${keypath} should be a number, if specified`);
		}
		return input;
	});
}

/**
 * @param {boolean} fallback
 * @returns {Validator}
 */
function boolean(fallback) {
	return validate(fallback, (input, keypath) => {
		if (typeof input !== 'boolean') {
			throw new Error(`${keypath} should be true or false, if specified`);
		}
		return input;
	});
}

/**
 * @param {string[]} options
 * @returns {Validator}
 */
function list(options, fallback = options[0]) {
	return validate(fallback, (input, keypath) => {
		if (!options.includes(input)) {
			// prettier-ignore
			const msg = options.length > 2
				? `${keypath} should be one of ${options.slice(0, -1).map(input => `"${input}"`).join(', ')} or "${options[options.length - 1]}"`
				: `${keypath} should be either "${options[0]}" or "${options[1]}"`;

			throw new Error(msg);

View on GitHub (pinned to 03f1687fe6)

Solutions

1. Use literal true or false (unquoted) in the config.
2. Convert env values explicitly: crawl: process.env.PRERENDER !== 'false'.
3. Delete the key to use the documented default.

Example fix

// before
kit: { prerender: { crawl: 'true' } }
// after
kit: { prerender: { crawl: true } }

const crawl = cfg.kit?.prerender?.crawl;
if (crawl !== undefined && typeof crawl !== 'boolean') throw new Error(`crawl should be a boolean, got ${typeof crawl}`);

function isBooleanOrUndefined(v) { return v === undefined || typeof v === 'boolean'; }

try {
  validateOptions(cfg);
} catch (e) {
  if (String(e.message).includes('should be true or false')) {
    console.error('Boolean flag has non-boolean value:', e.message);
    process.exit(1);
  } else throw e;
}

When it happens

Trigger: Setting kit.prerender.crawl: 'false' (string) or crawl: 0 / crawl: null in svelte.config.js, then triggering config validation via build or dev.

Common situations: Boolean flags sourced from environment variables (process.env.PRERENDER is the string 'false'), or hand-edited configs quoting the value.

Related errors

• ${keypath} must be an array of strings, if specified
• ${keypath} should be a number, if specified
• ${keypath} must be a valid origin — received '${input}' whic
• Each member of ${keypath} must be either '*' or an absolute
• Unexpected option ${keypath}.${key} (did you mean config.${k

AI-assisted analysis of sveltejs/kit@03f1687fe6 (2026-09-02). Data as JSON: /api/errors/913f6efd8effe7b0. Report an issue: GitHub.