UUID Generator: How to Generate Unique Identifiers for Databases, APIs, and Distributed Systems

A UUID (Universally Unique Identifier) is a 128-bit number used to uniquely identify information in computer systems. Unlike auto-incrementing IDs, UUIDs are designed to be globally unique across all systems and time — no central coordination needed. This makes them essential for distributed systems, databases, APIs, and anywhere you need to avoid ID collisions. Use the UUID Generator on TodayCalculator to create UUIDs in multiple versions instantly, with bulk generation support.

What Does a UUID Look Like?

A standard UUID is a 36-character string with 32 hexadecimal digits grouped as 8-4-4-4-12, like this:

550e8400-e29b-41d4-a716-446655440000

The hyphens are purely for readability — the underlying value is a 128-bit number. Because UUIDs are generated from your machine’s timestamp, random bits, and/or MAC address, the chance of two systems ever producing the same UUID is astronomically small.

UUID Versions: Which One Should You Use?

There are several UUID versions, and they’re not interchangeable — each exists to solve a different problem:

Version	Based On	Best For	Downside
v1	Timestamp + MAC address	Time-ordered IDs, traceability	Leaks MAC address; not fully random
v4	Random numbers	Most applications (default choice)	Not sortable by creation time
v5	SHA-1 hash of namespace + name	Deterministic IDs (same input → same UUID)	Requires careful namespace management
v7	Timestamp + random	Sortable UUIDs, database indexes	Newer, less tooling support

v4 is the safe default for most use cases. Choose v1 if you need time ordering, v5 if you need the same input to always produce the same UUID (e.g. deduplication), and v7 if you’re building a new database and want index-friendly sortable IDs.

UUID vs Auto-Increment ID

Criteria	UUID	Auto-Increment
Uniqueness scope	Global (works offline, across servers)	Local to one table/database
Security	Unpredictable — can’t be enumerated	Guessable — exposes record counts
Merge-friendly	Yes, no conflicts when merging data	No — IDs collide across sources
Index performance	Slower with v4 (random order)	Faster (sequential)
Storage size	16 bytes (128-bit)	4-8 bytes

Use UUIDs when data will be created on multiple clients or servers (mobile apps, offline sync, distributed services) or when you don’t want IDs to be guessable. Use auto-increment when you need maximum performance in a single-node database and IDs never leave the system.

How to Generate UUIDs

You don’t need to write code to generate UUIDs:

1. Open the UUID Generator
2. Choose the version (v4 is the default)
3. Pick how many UUIDs you need — the tool supports bulk generation of 1 to 100+ at once
4. Copy the result as lowercase, uppercase, or with/without hyphens

In code, most languages have a built-in option: Python’s uuid.uuid4(), JavaScript’s crypto.randomUUID(), or the uuid package in Go, Java, and C#.

Common UUID Use Cases

• Database primary keys — especially for tables that sync across devices
• API request IDs — trace a request through logs from client to server
• Order/cart identifiers — generated client-side before checkout
• File and blob names — avoid collisions in cloud storage buckets
• Session and token identifiers — unpredictable values are harder to guess

Generate your next batch of unique identifiers for free with the UUID Generator — no signup, no limits, bulk output supported.