12-Hour Time (H:MM AM/PM) Regex for Go

What this pattern does

This page provides a well-structured, multi-part regular expression for matching 12-hour time (h:mm am/pm), 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

// 12-Hour Time (H:MM AM/PM)
// ReDoS-checked | RegexVault — Localization > Time Formats

package validation

import "regexp"

var 12hourTimeHmmAmpmRe = regexp.MustCompile(`^(1[0-2]|0?[1-9]):([0-5][0-9])(?::([0-5][0-9]))?\s?(AM|PM|am|pm|Am|Pm)$`)

func Validate12hourTimeHmmAmpm(s string) bool {
    return 12hourTimeHmmAmpmRe.MatchString(s)
}

// Example
// fmt.Println(Validate12hourTimeHmmAmpm("12:30 PM")) // true

Test Cases

When to use this pattern

This pattern is drawn from the Localization > Time Formats 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

12:00 AM = midnight, 12:00 PM = noon — the most commonly confused values. 12-hour format is standard in US, UK, Australia, and parts of Asia. Many others use 24-hour exclusively.