DNS Name Length Checker

Validate DNS names against RFC length limits: 63 bytes per label, 255 bytes per FQDN

Label Limits: Each DNS label must be 63 characters or fewer.

FQDN Limits: Complete domain names must be 255 characters or fewer.

Compliance: Exceeding limits causes DNS resolution failures.

Name Length Examples

Zone File Content

DNS Name Limits

DNS names have strict length limits defined by RFC specifications. Each label (part between dots) must be 63 octets or less, and the complete FQDN must not exceed 255 octets including the length encoding.

Impact of Violations

Names exceeding these limits will cause DNS resolution failures. Some resolvers may truncate names, while others will reject them entirely. This can break applications and services relying on these names.

Common Causes

Long names often result from deep subdomain structures, verbose naming conventions, or automated name generation. Consider shorter alternatives or restructuring your DNS hierarchy to stay within limits.

Best Practices

Use concise, descriptive names. Avoid unnecessary subdomains and overly verbose labels. Regularly validate zone files during development. Consider using aliases or redirects for shorter public-facing names.