Last updated: March 2026
What is a UUID?
A UUID (Universally Unique Identifier) is a 128-bit identifier used to uniquely tag information in distributed systems without requiring a central coordinating authority. They're formatted as 32 hexadecimal digits in five groups separated by hyphens.
UUID v4, the most commonly used version, generates identifiers from random numbers with a collision probability so low it would take generating 1 billion UUIDs per second for 85 years to have a 50% chance of one duplicate.
UUIDs are used everywhere in software: database primary keys, API request IDs, session tokens, file identifiers, and distributed system coordination. Their key advantage is that any system can generate a UUID independently with virtually zero collision risk.
How to Generate UUIDs
Step 1: Choose your UUID version — v4 (random) for general use, v7 for database-optimized, or v1 for timestamp-based.
Step 2: Set the quantity (1 to 100) and format (lowercase, uppercase, no hyphens, braces, or URN).
Step 3: Click Generate — copy individual UUIDs, copy all, or download as a text file.
Key Features
Three UUID Versions. Generate v1 (timestamp-based), v4 (fully random), and v7 (timestamp-ordered random). Most generators only support v4 — we support all three modern versions with proper bit-level implementation.
Bulk Generation. Generate up to 100 UUIDs at once with quick-select buttons. Each UUID gets its own copy button, plus bulk copy and download options for large batches.
UUID Decoder. Paste any UUID to decode its version, variant, timestamp (for v1 and v7), clock sequence, and node. Validates format and structure instantly.
Cryptographic Quality. All UUIDs are generated using crypto.getRandomValues() for cryptographically secure randomness. Everything runs in your browser — no UUIDs are sent to any server.
UUID Versions Explained
Version 1 encodes the current timestamp (100-nanosecond intervals since October 15, 1582) and a node identifier (traditionally the MAC address, but we use random bytes for privacy). V1 UUIDs are time-sortable and you can extract the creation timestamp from them. The downside: they can leak timing information.
Version 4 is the most widely used — 122 bits of cryptographically random data with version and variant bits set. Simple to generate, impossible to predict, and has no information leakage. The only downside is that v4 UUIDs are randomly distributed, which can cause B-tree fragmentation in databases.
Version 7 is the newest standard (RFC 9562, 2024). It puts a Unix millisecond timestamp in the first 48 bits, followed by random data. This gives you the best of both worlds: time-sortable IDs that improve database index performance, with enough randomness to prevent collisions. V7 is the recommended choice for new database schemas.
Frequently Asked Questions
What is a UUID?
A UUID (Universally Unique Identifier) is a 128-bit identifier used to uniquely identify information in computer systems. Formatted as 32 hexadecimal digits in five groups separated by hyphens (e.g., 550e8400-e29b-41d4-a716-446655440000). UUIDs are used as database primary keys, API identifiers, session tokens, and more.
What is the difference between UUID and GUID?
UUID and GUID (Globally Unique Identifier) are essentially the same thing. UUID is the standard term used in RFC 4122 and most programming contexts. GUID is Microsoft's term used in Windows, .NET, and COM. They follow the same format and generation algorithms. Use whichever term your platform prefers.
Which UUID version should I use?
Use v4 (random) for most general purposes — it's the most widely used and simplest. Use v7 (timestamp + random) for database primary keys because it's sortable by creation time, which improves index performance. Use v1 (timestamp) when you need to extract creation time from the UUID itself.
Are UUIDs truly unique?
Practically yes. A v4 UUID has 122 random bits, giving 5.3 × 10³⁶ possible values. The probability of generating two identical v4 UUIDs is astronomically low — you'd need to generate 2.71 × 10¹⁸ UUIDs for a 50% chance of a single collision. In practice, UUID collisions don't happen.
What is UUID v7?
UUID v7 is the newest UUID version defined in RFC 9562 (2024). It combines a Unix timestamp in milliseconds (48 bits) with random data. This makes v7 UUIDs sortable by creation time while maintaining randomness. It's ideal for database primary keys because timestamp-ordered IDs improve B-tree index performance.
How many possible UUIDs are there?
A v4 UUID has 122 bits of randomness, giving 2¹²² ≈ 5.3 × 10³⁶ possible values. That's 5.3 undecillion. To put it in perspective: if every person on Earth generated 1 billion UUIDs per second, it would take about 100 billion years to exhaust all possible v4 UUIDs.