Click Generate to instantly create one or more UUID v4 identifiers. Set the count to up to 100 for bulk generation. All UUIDs are generated in your browser using crypto.randomUUID() — nothing is sent to any server.
What is a UUID?
A UUID (Universally Unique Identifier), also called a GUID (Globally Unique Identifier) on Windows, is a 128-bit identifier standardised in RFC 4122. It is represented as 32 hexadecimal digits in five groups separated by hyphens: xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx. UUIDs are designed to be globally unique without requiring a central coordination server.
A UUID v4 looks like: 550e8400-e29b-41d4-a716-446655440000. The third group's first digit (4) identifies it as version 4. The fourth group's first digit (8, 9, a, or b) identifies the variant.
UUID versions comparison
v1 — Timestamp + MAC address
Encodes the current time and the host's network interface MAC address. Monotonically increasing. Privacy risk (MAC address exposed).
v3 / v5 — Name-based (deterministic)
Generated by hashing a namespace UUID + name string (MD5 for v3, SHA-1 for v5). Same input always produces the same UUID — useful for content-addressable identifiers.
v4 — Random (most common)
122 random bits from a CSPRNG. No timestamp, no MAC address. Statistically unique — the odds of two v4 UUIDs colliding are astronomically low.
v7 — Sortable timestamp + random
A newer standard combining a millisecond-precision timestamp prefix with random bits. Produces time-sortable UUIDs, which are more efficient for database indexes than v4.
Code examples
JavaScript (browser / Node.js 19+)
// Single UUID
const id = crypto.randomUUID();
// e.g. "550e8400-e29b-41d4-a716-446655440000"
// Bulk
const ids = Array.from({ length: 10 }, () => crypto.randomUUID());
Python
import uuid
# UUID v4
print(uuid.uuid4()) # random
print(str(uuid.uuid4())) # as string
# UUID v5 (name-based, deterministic)
ns = uuid.NAMESPACE_DNS
print(uuid.uuid5(ns, 'example.com'))
Frequently asked questions
How unique is a UUID v4?
UUID v4 has 122 random bits. The probability of a collision among 1 billion generated UUIDs is approximately 1 in 2.7 × 10¹⁷. For all practical purposes, collisions will never occur.
Is this UUID generator cryptographically secure?
Yes. The browser's crypto.randomUUID() uses the operating system's CSPRNG (e.g. /dev/urandom on Linux, BCryptGenRandom on Windows).
Can I use UUIDs as database primary keys?
Yes, and it's common in distributed systems. The tradeoff versus auto-increment integers: UUIDs are 16 bytes (vs 4 for INT), and random v4 UUIDs fragment B-tree indexes. UUID v7 (sortable) largely solves the index fragmentation problem.
What is a GUID and how is it different from a UUID?
GUID (Globally Unique Identifier) is Microsoft's term for the same concept. GUIDs follow the UUID v4 format and are interchangeable with UUIDs in practice. Microsoft often formats GUIDs in uppercase with braces: {550E8400-...}.
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