UUID Generator Guide: Everything You Need to Know About Unique Identifiers

Every database record, every user session, every distributed transaction needs something to uniquely identify it. You could use auto-incrementing integers, but those break across multiple databases. You could use timestamps, but they reveal information about when things were created. What you need is a universally unique identifier—a UUID.

This guide covers everything from what UUIDs actually are to how to generate them and when to use each version.

What Is a UUID?

UUID stands for Universally Unique Identifier. It is a 128-bit number formatted as a string of 36 characters (32 hex digits plus 4 hyphens):

550e8400-e29b-41d4-a716-446655440000

The beauty of UUIDs is that you can generate them independently on different systems—across different servers, different databases, even different continents—without coordination. The probability of collision is astronomically low. We are talking about numbers so large that generating a billion UUIDs per second for centuries still would not give you a 50 percent chance of a single duplicate.

Our UUID Generator handles all common UUID versions instantly.

Understanding UUID Versions

Not all UUIDs are created equal. The specification defines several versions, each with different properties:

UUID Version 1: Time-Based

Combines the current timestamp and MAC address to create the identifier. The problem? It reveals when the UUID was created (bad for privacy) and exposes your MAC address (worse for security).

UUID Version 4: Random

The most common version. Generates 122 bits of randomness. No timestamp, no MAC address, just pure entropy. Perfect for most use cases. This is what most people mean when they say UUID.

UUID Version 7: Time-Ordered (New Standard)

The newer kid on the block, designed for databases. Like version 1, it is time-based, but it uses a timestamp with a random component. The key advantage: UUIDs generated later are lexically greater than earlier ones—this makes database indexing dramatically more efficient.

Other Versions

• Version 2: DCE Security variant (rarely used)
• Version 3: Name-based using MD5 (deterministic but deprecated)
• Version 5: Name-based using SHA-1 (deterministic but deprecated)

When to Use Each UUID Version

Here is a practical breakdown:

Use UUID Version 4 When:

• You need maximum unpredictability
• Privacy matters (no timestamps)
• You are generating identifiers in untrusted environments
• General-purpose unique IDs for any application

Use UUID Version 7 When:

• Database performance is critical
• You want sortability (great for B-tree indexes)
• Time-ordered IDs help with debugging
• You are building modern distributed systems

Avoid Version 1 Because:

• It exposes your MAC address
• Creates privacy concerns
• Reveals exact creation timestamp

UUIDs in Different Programming Languages

JavaScript

Modern browsers support the built-in function for generating random UUIDs. For server-side JavaScript (Node.js) or older browsers, you can use the uuid npm package with the appropriate version method.

Python

Python provides built-in support for generating random UUIDs through the uuid module. You can call the version 4 function directly.

Java

Java offers built-in UUID generation through the standard library. Simply call the static method that generates random UUIDs.

SQL Databases

Most modern databases provide functions for generating random UUIDs. PostgreSQL and MySQL 8+ both have built-in support for this.

Database Performance Considerations

Here is where things get interesting. UUIDs can be database performance traps if you are not careful.

The Problem with Random UUIDs in Databases

Random UUIDs (version 4) are terrible for B-tree indexes. Each new UUID scatters to a random position in the index, causing:

• Excessive page splits
• Index fragmentation
• Write amplification
• Slower inserts over time

The Solution: UUID Version 7

UUID version 7 fixes this by making the first portion time-based. New UUIDs cluster together, reducing index thrash. If your database supports version 7, use it for primary keys.

Alternative Strategies

ULIDs (Universally Unique Lexicographically Sortable Identifier): Another format that sorts lexicographically while preserving time ordering.

Snowflake-style IDs: Twitter is approach uses timestamp plus machine ID plus sequence. Great for distributed systems.

Composed keys: Sometimes simpler is better—use natural keys when they exist (email, username) and compound keys otherwise.

Practical Use Cases

User IDs

Generate a random UUID and store it as the unique identifier for each user in your system.

Session Tokens

Create random session tokens for user authentication. Store them in your database and associate with user accounts.

API Keys

Generate random API keys for developer access. Consider adding a purpose prefix to distinguish between different key types.

Distributed IDs

For microservices architecture, consider including a source identifier in your IDs to track which service created each record.

UUID Generator Tools

While programming languages provide UUID generation, dedicated tools offer more flexibility:

• Batch generation: Create multiple UUIDs at once
• Version selection: Choose version 4, version 7, or other versions
• Format options: Standard, uppercase, no dashes, URL-safe
• Validation: Check if existing strings are valid UUIDs
• Conversion: Transform between formats

Our UUID Generator handles all of this in your browser. For related identity tools, check out our Password Generator and Hash Generator.

Common Mistakes to Avoid

Using Version 1 in User-Facing Contexts

Never expose version 1 UUIDs to users—they reveal when accounts were created and expose MAC addresses.

Comparing UUIDs as Strings Without Normalizing

Different UUID representations might look equal but have case differences. Always normalize before comparing.

Using Random UUIDs as Database Primary Keys

On databases with B-tree indexes, version 4 UUIDs cause performance degradation. Use version 7 or consider different strategies.

Not Validating Input

If users submit UUIDs, validate them before using them in queries or storage.

UUIDs vs. Alternatives

Frequently Asked Questions

Key Takeaways

• UUIDs provide globally unique 128-bit identifiers that can be generated independently across systems
• UUID version 4 (random) is the most common choice for general-purpose unique identifiers
• UUID version 7 (time-ordered) is better for database primary keys due to better index performance
• Avoid UUID version 1—it exposes timestamps and MAC addresses, creating privacy and security issues
• Consider performance implications when using UUIDs in databases; version 7 is preferred for indexed columns

Generate unique identifiers instantly with our free UUID Generator tool.