To suppress or handle this error, implement `${name}` in htt

Error message

To suppress or handle this error, implement `${name}` in https://svelte.dev/docs/kit/configuration#prerender

What it means

During `vite build` prerendering, when a prerender error occurs and no prerender.<errorHandler> option is configured, SvelteKit logs the failure and this hint telling you to implement the named handler (e.g. handleHttpError, handleMissingId) in svelte.config.js, then aborts the build via the internal '__handled__' error.

Source

Thrown at packages/kit/src/core/postbuild/prerender.js:107

			const message = format(details);
			log.error(`\n${message}\n`);
		}

		switch (input) {
			case 'fail':
				return (details) => {
					log_failure(details);
					throw_handled();
				};
			case 'warn':
				return log_failure;
			case 'ignore':
				return noop;
			case undefined: {
				return (details) => {
					log_failure(details);

					log.err(
						`To suppress or handle this error, implement \`${name}\` in https://svelte.dev/docs/kit/configuration#prerender\n`
					);

					throw_handled();
				};
			}
			default:
				return (details) => {
					const message = format(details);

					try {
						// @ts-expect-error TS thinks T might be of a different kind, but it's not
						input({ ...details, message });
					} catch (error) {
						log.prettyError(error, import.meta.dirname);
						throw_handled();
					}
				};

View on GitHub (pinned to 03f1687fe6)

Solutions

Read the failure details logged just above the hint to find the offending route/link.
Implement the named handler (e.g. prerender.handleHttpError) in svelte.config.js returning 'fail', 'warn', or 'ignore' as desired.
Fix the underlying broken link or endpoint so the error disappears.

Example fix

// before (svelte.config.js)
prerender: { handleHttpError: undefined }
// after
prerender: {
  handleHttpError: ({ path, message }) => {
    if (path.startsWith('/legacy')) return; // ignore
    throw new Error(message);
  }
}

Defensive patterns

Strategy: validation

Validate before calling

// svelte.config.js — ensure every prerender error class has an explicit handler
const required = ['handleHttpError', 'handleMissingId', 'handleEntryGeneratorMismatch', 'handleNotPrerenderedRoute', 'handleInvalidUrl'];
for (const k of required) {
  if (!(k in config.prerender)) console.warn(`prerender.${k} is not configured`);
}

Try / catch

try {
  await build();
} catch (err) {
  if (err.message.includes('To suppress or handle this error')) {
    console.error('Configure prerender handlers in svelte.config.js; see logged failure details above');
  }
  throw err;
}

Prevention

Explicitly configure all prerender.handle* options instead of relying on defaults.
Fix broken links/404 endpoints reported during prerender rather than silencing them globally.
Run prerender-heavy builds locally before CI.

When it happens

Trigger: Prerendering hits an error (HTTP error response, missing id in an anchor, entry-generator mismatch, not-prerendered route, or invalid URL fetched from a page) while svelte.config.js has no corresponding `prerender.handle*` callback defined.

Common situations: A page links to a missing route or fetches a non-200 URL during prerender; CI builds fail with the hint message after the logged failure details.

Related errors

AI-assisted analysis of sveltejs/kit@03f1687fe6 (2026-09-02). Data as JSON: /api/errors/4c2f9140a6600819. Report an issue: GitHub.