Could not generate a valid regex from the remotePattern "${J

Error message

Could not generate a valid regex from the remotePattern "${JSON.stringify(pattern)}". Please check the syntax.

What it means

The Netlify adapter converts each config.image.remotePatterns entry into a JavaScript regex so it can be written into Netlify's image CDN configuration (remotePatternToRegex). Before handing the regex off, it sanity-compiles it with new RegExp(); if construction throws, the pattern is unusable, this warning prints, and the pattern is skipped (returns undefined), so those remote images will not be optimized.

Source

Thrown at packages/integrations/netlify/src/index.ts:111

			// Exact match
			regexStr += `(${escapeRegex(pathname)})`;
		}
	} else {
		// Default to matching any path
		regexStr += '(\\/[^?#]*)?';
	}
	if (!regexStr.endsWith('.*)')) {
		// Match query, but only if it's not already matched by the pathname
		regexStr += '([?][^#]*)?';
	}
	// Anchor to end of string so .test() can't match a prefix
	regexStr += '$';
	try {
		// nosemgrep: javascript.lang.security.audit.detect-non-literal-regexp.detect-non-literal-regexp
		// This only validates the generated pattern before handing it to Netlify.
		new RegExp(regexStr);
	} catch {
		logger.warn(
			`Could not generate a valid regex from the remotePattern "${JSON.stringify(
				pattern,
			)}". Please check the syntax.`,
		);
		return undefined;
	}
	return regexStr;
}

function remoteImagesFromAstroConfig(
	config: AstroConfig,
	logger: AstroIntegrationLogger,
): string[] {
	const remoteImages: string[] = [];
	// Domains get a simple regex match
	remoteImages.push(
		...config.image.domains.map((domain) => `^https?:\/\/${escapeRegex(domain)}\/.*$`),
	);

View on GitHub (pinned to 3578d45d34)

Solutions

Inspect the printed remotePattern JSON and fix field values: protocol like 'https', hostname optionally prefixed with '**.' or '*.', numeric port, pathname using only trailing '/**' or '/*' wildcards.
Move simple hostnames into image.domains instead of remotePatterns when no path/port matching is needed.
Test the pattern locally with a tiny regex rebuild, or just run astro build again to confirm no warning prints and the images are served through the CDN.
If you need regex-level control, verify each segment escapes metacharacters yourself before putting the literal in config.

Example fix

// before (astro.config.mjs)
image: {
  remotePatterns: [{ protocol: 'https', hostname: 'cdn.example.com', port: '80-443' }],
},

// after
image: {
  remotePatterns: [{ protocol: 'https', hostname: 'cdn.example.com' }],
},

Defensive patterns

Strategy: validation

Validate before calling

const isValidRemotePattern = (p: {
  protocol?: string;
  hostname?: string;
  port?: string | number;
  pathname?: string;
}): boolean =>
  (!p.protocol || /^[a-z]+$/i.test(p.protocol)) &&
  (!p.hostname || /^\*?\*?\.?[a-z0-9.*-]+$/i.test(p.hostname)) &&
  (p.port === undefined || /^\d+$/.test(String(p.port))) &&
  (!p.pathname || /^\/.*/.test(p.pathname));

const allPatternsValid = config.image.remotePatterns.every(isValidRemotePattern);

Type guard

interface RemotePattern {
  protocol?: string;
  hostname?: string;
  port?: string | number;
  pathname?: string;
}
const isRemotePattern = (p: unknown): p is RemotePattern =>
  typeof p === 'object' && p !== null &&
  Object.keys(p).every((k) => ['protocol', 'hostname', 'port', 'pathname'].includes(k));

Prevention

Keep port numeric and omit it when unnecessary.
Use only the supported wildcard forms: '**.' prefix on hostname, trailing '/**' or '/*' on pathname.
Prefer image.domains for plain hostnames and reserve remotePatterns for path/port matching.
Watch build logs for this warning after every image config change; a skipped pattern means unoptimized remote images.

When it happens

Trigger: An entry in image.remotePatterns whose fields produce an invalid regex: e.g. a port that is not numeric ('port: "80:90"' interpolated raw into ':80:90'), a protocol with regex metacharacters, or a malformed pattern object. The catch around new RegExp(regexStr) in remotePatternToRegex fires and the function returns undefined.

Common situations: Typos in remotePatterns objects; port given as a range or non-numeric string; assuming remotePatterns supports full regex syntax when it only supports the **. and /* wildcard conventions; copying patterns from next.config.js where semantics differ slightly.

Related errors

AI-assisted analysis of withastro/astro@3578d45d34 (2026-08-18). Data as JSON: /api/errors/9b4ca550d006b9d1. Report an issue: GitHub.