UUID v4 Generator

What is UUID Version 4?

UUID version 4 (also known as random UUID) is a unique identifier generated entirely using random or pseudo-random numbers. Unlike UUID v1 which uses timestamps, or UUID v5 which uses hashing, UUID v4 relies solely on randomness for uniqueness.

Of the 128 bits in a UUID v4, 122 bits are randomly generated. The remaining 6 bits are used to indicate the version (4 bits set to "0100" for version 4) and variant (2 bits set to "10" for RFC 4122). This means there are 2¹²² (approximately 5.3 × 10³⁶) possible UUID v4 values.

UUID v4 is the most commonly used UUID version in modern software development due to its simplicity, privacy benefits, and excellent collision resistance. Our generator uses the browser's Web Crypto API to ensure cryptographically secure random number generation.

UUID v4 Structure

A UUID v4 follows the standard UUID format with specific bits reserved for version and variant identification:

Example UUID v4: f47ac10b-58cc-4372-a567-0e02b2c3d479

You can always identify a UUID v4 by checking that:

• The 13th character (first character of the third group) is "4"
• The 17th character (first character of the fourth group) is "8", "9", "a", or "b"

Use our UUID Validator to automatically detect the version of any UUID.

How Random is UUID v4? Understanding Collision Probability

UUID v4's uniqueness comes from the extreme improbability of generating the same random number twice. With 122 random bits, the math works strongly in your favor:

Real-World Perspective

• • 1 billion UUIDs/second: 86 years to reach 50% collision probability
• • Every human on Earth: Could each generate 600 million UUIDs before 50% collision chance
• • Your application: Even generating 1 million UUIDs per day for 100 years, collision probability is ~10^-24

When to Use UUID v4

UUID v4 is the best choice for most applications. Here's when you should (and shouldn't) use it:

UUID v4 vs Other UUID Versions

Generate UUID v4 in Code

UUID v4 has excellent native support across programming languages. Here's how to generate them:

// Native browser API (Chrome 92+, Firefox 95+, Safari 15.4+)
const uuid = crypto.randomUUID();
console.log(uuid);  // e.g., "f47ac10b-58cc-4372-a567-0e02b2c3d479"

// Node.js 19+ also supports crypto.randomUUID()
import { randomUUID } from 'crypto';
const id = randomUUID();

import uuid

# Generate UUID v4
my_uuid = uuid.uuid4()
print(my_uuid)  # e.g., f47ac10b-58cc-4372-a567-0e02b2c3d479

# Convert to string without hyphens
print(my_uuid.hex)  # f47ac10b58cc4372a5670e02b2c3d479

import java.util.UUID;

// Generate UUID v4 - built into Java since 1.5!
UUID uuid = UUID.randomUUID();
System.out.println(uuid);  // e.g., f47ac10b-58cc-4372-a567-0e02b2c3d479

// Get as string
String uuidString = uuid.toString();

// Generate GUID (Microsoft's name for UUID v4)
Guid guid = Guid.NewGuid();
Console.WriteLine(guid);  // e.g., f47ac10b-58cc-4372-a567-0e02b2c3d479

// Format options
Console.WriteLine(guid.ToString("N"));  // No hyphens
Console.WriteLine(guid.ToString("B"));  // With braces {}

import "github.com/google/uuid"

// Generate UUID v4
id := uuid.New()
fmt.Println(id.String())  // e.g., f47ac10b-58cc-4372-a567-0e02b2c3d479

// Or generate with explicit v4 function
id = uuid.NewRandom()

More language guides: PHP, Ruby, Rust, Swift, Kotlin, TypeScript, Bash.

UUID v4 in Databases

While UUID v4 works in any database, there are some performance considerations to be aware of:

-- PostgreSQL 13+ has gen_random_uuid() built-in
CREATE TABLE users (
    id UUID DEFAULT gen_random_uuid() PRIMARY KEY,
    email VARCHAR(255) NOT NULL
);

-- Insert with auto-generated UUID
INSERT INTO users (email) VALUES ('[email protected]');

-- Or generate in query
SELECT gen_random_uuid();

-- Note: MySQL's UUID() generates v1, not v4
-- For v4, generate in application code or use:
CREATE TABLE users (
    id BINARY(16) PRIMARY KEY,
    email VARCHAR(255) NOT NULL
);

-- Insert with application-generated UUID v4
INSERT INTO users (id, email) 
VALUES (UUID_TO_BIN('f47ac10b-58cc-4372-a567-0e02b2c3d479'), '[email protected]');

Security Considerations

While UUID v4 provides excellent uniqueness and unpredictability, always use appropriate security measures for your specific use case. A UUID alone shouldn't be your only security mechanism.

Related UUID Tools

Frequently Asked Questions