UUID Guide: What is UUID & Version 4 Explained

What is a UUID?

UUID (Universally Unique Identifier) is a 128-bit number used to identify information in computer systems. The term GUID (Globally Unique Identifier) is also used, especially by Microsoft. A standard UUID looks like: 550e8400-e29b-41d4-a716-446655440000

UUID Version 4

UUID v4 uses random numbers to generate the identifier. The structure includes:

• Version bits: Characters 13-14 are always "4"
• Variant bits: Characters 17-18 are 8, 9, A, or B
• Remaining bits: Randomly generated

With 2^122 possible random UUIDs, collisions are extremely unlikely.

Use Cases in Applications

• Database primary keys: Avoid auto-increment collision in distributed systems
• File uploads: Generate unique filenames
• Session IDs: User session tracking
• Transaction IDs: Payment and order tracking
• Microservices: Correlate requests across services