UUID Generator: How to Generate and Use Unique Identifiers for Your Development Projects

Universally Unique Identifiers, or UUIDs, are 128-bit numbers used to uniquely identify information in computer systems. They are everywhere in modern software — database primary keys, API resource identifiers, session tokens, file names, and distributed system records. Unlike auto-incrementing IDs, UUIDs can be generated independently on any machine without coordination or central authority. Use the UUID Generator at Today Calculator to create UUIDs instantly in your browser.

What Are UUIDs and Why Use Them?

A UUID is a string formatted as 32 hexadecimal digits separated by hyphens into five groups: 8-4-4-4-12. For example: 550e8400-e29b-41d4-a716-446655440000. The total number of possible UUIDs is 2¹²⁸, or about 340 undecillion — so astronomically large that generating random UUIDs has an effectively zero chance of collision.

Feature	Auto-Increment ID	UUID
Uniqueness scope	Single database table	Global (everywhere)
Generation	Centralized (DB)	Decentralized (any client)
Predictable?	Yes (sequential)	No (random)
Size	4 bytes (int)	16 bytes (128 bits)
Merge-friendly?	No (conflicts)	Yes

UUID Versions Explained

• UUID v4 (Random) — Most common. 122 bits of random data. Used for session tokens, record IDs, and any system where randomness is acceptable. The Today Calculator UUID Generator produces v4 by default.
• UUID v1 (Time-based) — Combines timestamp + MAC address. Useful when IDs need to be sortable by creation time, but the MAC address can be a privacy concern.
• UUID v7 (Time-ordered) — Newer standard that combines timestamp with random bits. Sortable like v1 but without exposing MAC addresses. Ideal for database primary keys because they keep B-tree indexes efficient.

Common Use Cases

• Database primary keys — Especially in distributed databases where multiple servers insert records simultaneously without coordination
• API identifiers — REST resource IDs that should not reveal record counts or sequential patterns
• File and asset naming — Uploaded files renamed to UUIDs to avoid filename collisions
• Session and transaction IDs — Each session gets a unique, non-guessable identifier
• Offline-first applications — Mobile apps that generate IDs locally and sync later to a central database

Performance Considerations

UUIDs are 4x larger than integer IDs (16 bytes vs 4 bytes). This means larger indexes and slightly slower INSERT performance on very large tables. The trade-off is worth it when you need distributed generation, merge-friendly data, or opaque identifiers. For high-write-volume tables with millions of rows, consider UUID v7 (time-ordered) to minimize index fragmentation, or use a hybrid approach with auto-increment for internal IDs and UUIDs for external references.

Generate your next UUID instantly with the UUID Generator at Today Calculator. One click gives you a valid v4 UUID ready to paste into your code, database, or configuration file.