Networking

Hostname (Single Label, RFC 1123)

Validate a single-label hostname per RFC 1123: 1–63 chars, letters/digits/hyphens, can't start or end with hyphen.

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Available in

JSSupported

JavaScript / ECMAScript

Browser-native RegExp. Default if you don't pick.

PYSupported

Python (re)

CPython stdlib `re`. Unicode-aware `\w` and `\d` by default.

GOSupported

Go (RE2)

Linear-time matching. No backreferences or lookarounds.

Pattern

regexengine-agnostic
^[a-zA-Z0-9](?:[a-zA-Z0-9\-]{0,61}[a-zA-Z0-9])?$

Raw source: ^[a-zA-Z0-9](?:[a-zA-Z0-9\-]{0,61}[a-zA-Z0-9])?$

How it works

^[a-zA-Z0-9] requires the first character to be a letter or digit. (?:[a-zA-Z0-9\-]{0,61}[a-zA-Z0-9])? optionally matches up to 61 more characters (letters, digits, hyphens) followed by a letter/digit ending — preventing trailing hyphens. Combined max length: 63 characters per RFC 1123.

Examples

Input

web-01

Matches

  • web-01

Input

host123

Matches

  • host123

Input

-bad-start

No match

—

Common use cases

  • •Kubernetes pod and service name validation
  • •DNS label sanity checking
  • •Container hostname enforcement
  • •Server provisioning input validation
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