JSON Web Token (JWT) — Structure Validation Regex for Go

What this pattern does

This page provides a well-structured, multi-part regular expression for matching json web token (jwt) — structure validation, ported and verified for Go. In security-sensitive code, using an unverified regex can open the door to both false positives and denial-of-service attacks. 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

// JSON Web Token (JWT) — Structure Validation
// ReDoS-safe | RegexVault — Security > API Keys & Tokens

package validation

import "regexp"

var jsonWebTokenJwtStructureValidationRe = regexp.MustCompile(`^([A-Za-z0-9_-]+)\.([A-Za-z0-9_-]+)\.([A-Za-z0-9_-]+)$`)

func ValidateJsonWebTokenJwtStructureValidation(s string) bool {
    return jsonWebTokenJwtStructureValidationRe.MatchString(s)
}

// Example
// fmt.Println(ValidateJsonWebTokenJwtStructureValidation("eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJzdWIiOiIxMjM0NTY3ODkwIn0.SflKxwRJSMeKKF2QT4fwpMeJf36POk6yJV_adQssw5c")) // true

Test Cases

When to use this pattern

This pattern is drawn from the Security > API Keys & Tokens 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

Technical Notes

Structure only — does not validate header algorithm, payload claims, expiry, or signature. Three segments: header (base64url) + payload (base64url) + signature (base64url, may be empty for 'none' algorithm — always reject 'none'). Capture groups: 1=header, 2=payload, 3=signature.