Validate hostname

Check RFC 1123 hostname labels, lengths, and allowed hyphens.

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ToolHostname Validator
Input
Output
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How it works

The lowercased hostname is split into labels, checked against 63-character label and 253-character total limits, and each label must start and end with a letter or digit while allowing internal hyphens. A single label is allowed because no public TLD is required.

  • Numeric-leading labels are permitted by RFC 1123.
  • Lowercasing follows DNS case-insensitivity.

Worked example

Valid Hostname
Validate a well-formed hostname
Input
											web-server-01.us-east.example.com
Output
												Valid hostname: web-server-01.us-east.example.com

When to use this

Server configs, Kubernetes services, and TLS DNS names validate hostnames.

Edge cases

  • A label ending in a hyphen is invalid.
  • localhost is valid as a single host label here.
  • An underscore fails the host pattern despite some discovery systems using it.

References