Why You Should Use crypto.randomUUID() Instead of Math.random() for IDs

Math.random() is not random enough for IDs. Here's why — and what to use instead.

The Problem with Math.random()

Math.random() is a pseudo-random number generator (PRNG). It's deterministic: given the same seed, it produces the same sequence. The seed is usually the current timestamp.

This means:

• If two tabs initialize at the same millisecond, they can produce the same "random" values
• The sequence is predictable once you know the seed
• It's not suitable for security-sensitive IDs

crypto.randomUUID()

Available in all modern browsers and Node.js 14.17+:

const id = crypto.randomUUID();
// "550e8400-e29b-41d4-a716-446655440000"

This generates a v4 UUID using the operating system's cryptographically secure random number generator (CSPRNG) — the same source used for cryptographic keys.

Generating Multiple UUIDs

function generateUUIDs(count, options = {}) {
  const { uppercase = false, stripHyphens = false } = options;

  return Array.from({ length: count }, () => {
    let id = crypto.randomUUID();
    if (stripHyphens) id = id.replace(/-/g, '');
    if (uppercase) id = id.toUpperCase();
    return id;
  });
}

UUID v4 Structure

A UUID looks random but has structure:

xxxxxxxx-xxxx-4xxx-yxxx-xxxxxxxxxxxx
                ^    ^
                |    y is 8, 9, a, or b (variant bits)
                version (always 4 for v4)

The version and variant bits take up 6 of the 128 bits, leaving 122 bits of actual randomness. That's 2^122 possible values — collision probability is negligible.

Collision Probability

Generating 1 billion UUIDs per second, you'd expect your first collision after about 85 years. For practical applications, UUIDs are safe to generate independently without coordination.

When You Still Need a Server

UUIDs are great for client-generated IDs, but if you need sequential IDs (for database pagination), time-ordered IDs (UUIDv7), or guaranteed global uniqueness across distributed systems, the server is still the right place.

Generate UUIDs at toolzip.app/tools/uuid-generator.