What is the difference between UUID v1, v4, and v5?

UUID v4 is randomly generated — use it when you need a unique, unpredictable identifier (database primary keys, session IDs). UUID v1 is time-based and includes a machine identifier — useful when you need sortable IDs but avoid it when anonymity matters. UUID v5 is deterministic — given the same namespace and name, it always produces the same UUID — useful for content addressing and deduplication.

Are UUID v4 values guaranteed to be unique?

UUIDs are not mathematically guaranteed unique, but the probability of collision is astronomically low — roughly 1 in 5.3 × 10^36 for any two random v4 UUIDs. For all practical purposes, you can treat them as unique without any central coordination.

When should I use UUID instead of a database auto-increment ID?

Use UUIDs when you need IDs to be generated without database coordination (e.g., in distributed systems or client-side), when you don't want to expose sequential record counts to users, or when merging records from multiple databases. Use auto-increment IDs when performance and sortability are priorities and you have a single centralized database.

Is UUID the same as GUID?

Yes. GUID (Globally Unique Identifier) is Microsoft's term for what the RFC 4122 standard calls a UUID. They use the same format and are interchangeable. The only practical difference is that some Microsoft implementations historically generated v1-like UUIDs with different byte ordering.

Tool

UUID Generator

Generate RFC 4122 compliant UUIDs in Version 1 (time-based), Version 4 (random), and Version 5 (name-based) formats. Generate up to 100 at once.

Last updated March 1, 2026

Runs entirely in your browser — no data sent to servers. Privacy policy

Prove it runs locally

Open DevTools → Network tab
Click Generate
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Generation uses crypto.getRandomValues() in your browser. Privacy policy

UUID version

Count (1–100)

Generated UUIDs

Click "Generate UUIDs" to create identifiers.

RFC 4122 compliant v4 uses crypto.randomUUID().

Select the UUID version: v4 (random) is recommended for most use cases. v1 uses the current timestamp and machine identifier. v5 is deterministic — it generates the same UUID for the same name and namespace combination.

Set the quantity (1-100) to generate multiple UUIDs at once — useful for seeding databases or creating test data. For v5, enter your namespace UUID and name string.

Copy individual UUIDs with the copy button, or use the "Copy All" button to copy the entire list. UUIDs are formatted in the standard 8-4-4-4-12 hexadecimal pattern.

// Node.js 14.17+ has crypto.randomUUID() built-in
const { randomUUID } = require('crypto');

// v4 (random) — most common
const id = randomUUID();
console.log(id); // e.g., '9b1deb4d-3b7d-4bad-9bdd-2b0d7b3dcb6d'

// Using the 'uuid' package for v1, v5 support
const { v1, v4, v5 } = require('uuid');
console.log(v1()); // time-based
console.log(v4()); // random
console.log(v5('example.com', v5.DNS)); // deterministic

// Node.js 14.17+ has crypto.randomUUID() built-in
const { randomUUID } = require('crypto');

// v4 (random) — most common
const id = randomUUID();
console.log(id); // e.g., '9b1deb4d-3b7d-4bad-9bdd-2b0d7b3dcb6d'

// Using the 'uuid' package for v1, v5 support
const { v1, v4, v5 } = require('uuid');
console.log(v1()); // time-based
console.log(v4()); // random
console.log(v5('example.com', v5.DNS)); // deterministic

import uuid

# v4 — random
id_v4 = uuid.uuid4()
print(str(id_v4))  # e.g., '9b1deb4d-3b7d-4bad-9bdd-2b0d7b3dcb6d'

# v1 — time-based
id_v1 = uuid.uuid1()
print(str(id_v1))

# v5 — deterministic (DNS namespace)
id_v5 = uuid.uuid5(uuid.NAMESPACE_DNS, 'example.com')
print(str(id_v5))

import "github.com/google/uuid"

// v4 — random (most common)
id := uuid.New()
fmt.Println(id.String()) // e.g., '9b1deb4d-3b7d-4bad-9bdd-2b0d7b3dcb6d'

// v5 — deterministic
id5 := uuid.NewSHA1(uuid.NameSpaceDNS, []byte("example.com"))
fmt.Println(id5.String())

// Parse an existing UUID string
parsed, err := uuid.Parse("9b1deb4d-3b7d-4bad-9bdd-2b0d7b3dcb6d")

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