UUID Generator
Generate universally unique identifiers in all RFC 4122 versions — random, timestamp-based, and name-based.
Click Generate to create UUIDs
- Version
- Variant
- Normalized
NIL UUID (all zeros)
What is UUID v4?
UUID v4 generates 122 bits of random data using a cryptographically secure random number generator. It is the most common UUID version and the best choice when you don't need deterministic IDs.
Name-Based UUIDs (v3 & v5)
v3 uses MD5 and v5 uses SHA-1 to hash a namespace UUID + a name. Given the same inputs, they always produce the same UUID — making them ideal for reproducible IDs like resource identifiers.
When to use UUIDs?
UUIDs are used as primary keys in databases, unique file names, session tokens, API resource identifiers, and distributed system IDs. Unlike auto-increment integers, UUIDs work across multiple databases without coordination.
Frequently Asked Questions
Everything you need to know about UUIDs and their versions
A UUID (Universally Unique Identifier) is a 128-bit number formatted as 32 hexadecimal characters in the pattern xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx. UUIDs are used wherever you need unique IDs without a central authority — database primary keys, file names, session tokens, API resources, and distributed system IDs. The probability of generating the same UUID v4 twice is astronomically small: about 1 in 5.3 × 10^36.
UUID v1 uses the current timestamp + a random node identifier, making it partially sortable but revealing generation time. UUID v3 uses MD5 to hash a namespace + name — deterministic but MD5 is considered weak. UUID v4 is fully random and the most commonly used. UUID v5 uses SHA-1 to hash namespace + name — deterministic and stronger than v3. NIL is all zeros, used as a null/empty value.
For most applications, UUID v4 is the best choice — it is random, collision-resistant, and doesn't leak information. Use v5 when you need reproducible IDs from the same input (e.g. converting usernames to UUIDs deterministically). Use v1 only if you need time-sortable IDs and understand the timestamp information it encodes. Avoid v3 (MD5) in new systems.
UUID v4 has 122 random bits, giving 2^122 possible values (~5.3 × 10^36). At 1 billion UUIDs per second, you would need about 85 years to have a 50% probability of a single collision. For practical purposes, UUIDs are unique. UUID v3/v5 are deterministic — the same namespace+name always gives the same UUID, which is both a feature and a constraint.
Yes. This tool uses window.crypto.getRandomValues(), the same cryptographically secure random number generator used by browsers for TLS and other security functions. However, for session tokens or secrets, consider using the Token Generator tool instead — tokens are purely random, while UUIDs include version and variant bits that slightly reduce entropy.