What is a UUID?
A UUID (Universally Unique Identifier) is a 128-bit label standardised by RFC 4122, formatted as 32 hexadecimal digits split into five groups: xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx. UUIDs are designed to be globally unique without a central authority, making them ideal for distributed systems.
What is UUID v4?
UUID version 4 is generated entirely from random (or pseudo-random) bytes. Except for two fixed bits that indicate the version, all 122 remaining bits are random. The probability of two v4 UUIDs colliding is astronomically small — roughly 1 in 5.3 × 10³⁶ for any single pair.
How to generate a UUID?
Enter the number of UUIDs you need (1–100) and click Generate UUIDs. The results appear immediately, one UUID per line. Use the copy button to copy all UUIDs to your clipboard at once.
What are UUIDs used for?
UUIDs are used wherever globally unique identifiers are needed without central coordination: database primary keys, session tokens, file names, API resource IDs, device identifiers, and distributed system event IDs. They are supported natively in PostgreSQL, MongoDB, and most major programming languages. When your project also requires tracking creation timestamps, our date calculator can compute the exact span between any two dates. For generating random numbers outside the UUID format — such as numeric tokens or test data — our random number generator is a quick alternative.
What does a UUID look like in practice?
A UUID has the format xxxxxxxx-xxxx-4xxx-yxxx-xxxxxxxxxxxx where 4 indicates version 4 and y is one of 8, 9, a, or b (indicating the variant). Example: 550e8400-e29b-41d4-a716-446655440000.
Are UUIDs case-sensitive?
UUIDs are case-insensitive by specification. Both 550e8400-e29b-41d4-a716-446655440000 and 550E8400-E29B-41D4-A716-446655440000 refer to the same UUID. This generator outputs lowercase, which is the most common convention.
How do UUID versions differ from each other?
UUID v1 encodes a timestamp and the generating machine's MAC address, which can expose system information and makes it unsuitable for privacy-sensitive contexts. UUID v3 and v5 are name-based: they derive a deterministic UUID from a namespace and input string using MD5 (v3) or SHA-1 (v5) — the same input always produces the same UUID. UUID v4 (used here) is purely random and is the most widely used version. UUID v7 is an emerging standard that prefixes random bits with a millisecond timestamp, making UUIDs naturally sortable by creation time — a significant advantage for database index performance.