Wildcard Domain Regex for Go

What this pattern does

This page provides a well-structured, multi-part regular expression for matching wildcard domain, ported and verified for Go. A rigorously tested regex reduces debugging time and protects your application from edge-case failures. The snippet below is ready to drop into your Go project — whether you're validating in a Gin handler, a gRPC service, or a command-line tool.

Go Implementation

// Wildcard Domain
// ReDoS-checked | RegexVault — Web & Network > Domain

package validation

import "regexp"

var wildcardDomainRe = regexp.MustCompile(`^\*\.(?:[a-zA-Z0-9](?:[a-zA-Z0-9\-]{0,61}[a-zA-Z0-9])?\.)+[a-zA-Z]{2,63}$`)

func ValidateWildcardDomain(s string) bool {
    return wildcardDomainRe.MatchString(s)
}

// Example
// fmt.Println(ValidateWildcardDomain("*.example.com")) // true

Test Cases

When to use this pattern

This pattern is drawn from the Web & Network > Domain category and has been checked for ReDoS risk. That matters for Go developers because Go's RE2 engine is inherently safe from catastrophic backtracking, but this pattern has been additionally verified for correctness. RegexVault audits patterns against known backtracking attack vectors, ensuring you have the necessary context before using this regex in a high-stakes production environment.

Common Pitfalls

Technical Notes

Per RFC 2818 and CA/B Forum requirements, wildcard certificates cover only one label depth (*.example.com matches api.example.com but NOT deep.api.example.com). Multiple wildcards are invalid.