REGEXVAULTv2.0
Web & Network/Domain
Verified Safe

Domain Name with Subdomain Regex for Go

/^(?:[a-zA-Z0-9](?:[a-zA-Z0-9\-]{0,61}[a-zA-Z0-9])?\.){2,}[a-zA-Z]{2,63}$/i

What this pattern does

This page provides a well-structured, multi-part regular expression for matching domain name with subdomain, 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

Go
// Domain Name with Subdomain
// ReDoS-safe | RegexVault — Web & Network > Domain

package validation

import "regexp"

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

func ValidateDomainNameWithSubdomain(s string) bool {
    return domainNameWithSubdomainRe.MatchString(s)
}

// Example
// fmt.Println(ValidateDomainNameWithSubdomain("www.example.com")) // true

Test Cases

Matches (Valid)
Rejects (Invalid)
www.example.comexample.com
api.example.co.ukcom
sub.domain.example.net.example.com
mail.example.orgexample-.com
a.b.example.ioapi.example

When to use this pattern

This pattern is drawn from the Web & Network > Domain category and carries a ReDoS-safe certification. 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

Country-code TLDs with second-level domains (e.g., co.uk, com.au) will pass because they satisfy the dot-count requirement.

Technical Notes

The {2,} quantifier ensures at least one subdomain prefix exists before the SLD+TLD. Does not enforce TLD validity.

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