UUID Generator
Generate RFC 4122 version 4 UUIDs (GUIDs) using cryptographic randomness. Bulk generate up to 100 at a time.
How to Use the UUID Generator
- Set the count -- Choose how many UUIDs to generate (1 to 100).
- Choose display options -- Select uppercase or lowercase, and with or without hyphens.
- Generate -- Click the Generate button to create your UUIDs instantly.
- Copy -- Click "Copy All" to copy every UUID to your clipboard, one per line.
About UUIDs
A UUID (Universally Unique Identifier), also known as a GUID (Globally Unique Identifier), is a 128-bit identifier standardized by RFC 4122. The version 4 UUID generated here is created from cryptographically secure random numbers. The format is xxxxxxxx-xxxx-4xxx-yxxx-xxxxxxxxxxxx, where 4 indicates version 4 and y is constrained to 8, 9, a, or b to indicate the variant.
UUIDs are widely used in software development for database primary keys, distributed systems, session identifiers, and anywhere a unique identifier is needed without central coordination. With 122 bits of randomness, the chance of collision is negligibly small -- you would need to generate over a billion UUIDs per second for decades to have a 50% probability of a single collision.
Use Cases for UUIDs
UUIDs are fundamental building blocks in modern software development. Here are the most common scenarios where they are used.
Database Primary Keys
Using UUIDs as primary keys allows records to be created independently across multiple database nodes without risk of collision. This is essential in distributed databases, microservice architectures, and systems that merge data from multiple sources. Unlike auto-incrementing integers, UUIDs do not reveal the total number of records or the order in which they were created.
Distributed Systems and Microservices
In distributed architectures, different services need to generate unique identifiers without communicating with a central authority. UUIDs solve this problem elegantly -- each service generates its own identifiers with negligible collision probability, enabling independent operation and eventual consistency.
Session and Request Tracking
Web applications use UUIDs for session identifiers, request correlation IDs, and tracing tokens. Assigning a UUID to each request allows developers to trace it across multiple services in a microservice stack, making debugging and log analysis significantly easier.
File and Resource Naming
When users upload files or create resources, UUIDs provide collision-free naming without requiring database lookups. This is common in cloud storage systems, content management platforms, and media processing pipelines where filenames must be unique across millions of objects.
API Tokens and Temporary Identifiers
UUIDs serve as non-guessable identifiers for temporary resources like password reset tokens, email confirmation links, and single-use API keys. Their randomness makes them resistant to enumeration attacks where an attacker tries sequential IDs to discover valid resources.
UUID Version Comparison
The UUID specification defines several versions, each with different generation methods and properties. This tool generates Version 4 UUIDs, the most widely used variant.
| Version | Method | Random Bits | Best For |
|---|---|---|---|
| v1 | Timestamp + MAC address | 0 | Time-ordered IDs, legacy systems |
| v3 | MD5 hash of namespace + name | 0 | Deterministic IDs from names |
| v4 | Random | 122 | General purpose, most common |
| v5 | SHA-1 hash of namespace + name | 0 | Deterministic IDs (preferred over v3) |
| v7 | Unix timestamp + random | 62 | Time-ordered, database-friendly |
Version 4 is the most widely used because it requires no coordination, no timestamp, and no hardware address. It is generated purely from cryptographic randomness, making it the simplest and most portable option. Version 7 is a newer alternative that embeds a Unix timestamp, providing natural chronological ordering which improves database index performance.
Best Practices
When using UUIDs in production systems, consider the storage format carefully. Storing UUIDs as 16-byte binary values rather than 36-character strings reduces storage by more than half and improves index performance. Most databases support a native UUID column type that handles this efficiently.
If your application requires UUIDs that sort chronologically -- for example, when used as database primary keys in a B-tree index -- consider UUID v7 or ULID (Universally Unique Lexicographically Sortable Identifier) instead of v4. Random v4 UUIDs cause index fragmentation because inserts scatter across the tree, while time-ordered identifiers maintain locality and improve write throughput.
Never treat UUIDs as secret tokens. Although they are random and hard to guess, a UUID that has been shared in a URL, log file, or API response should be considered public. For authentication tokens or secrets, use purpose-built secure random generators with higher entropy and shorter lifetimes.
Frequently Asked Questions
A UUID (Universally Unique Identifier) is a 128-bit number used to uniquely identify information in computer systems. Version 4 UUIDs are generated from random numbers and have an extremely low probability of collision, making them ideal for distributed systems.
UUID and GUID are the same thing. UUID is the standard term (from IETF RFC 4122), while GUID is the name commonly used by Microsoft. They follow the same specification and format.
While theoretically possible, the probability is astronomically small. With 122 random bits, you would need to generate roughly 2.71 quintillion UUIDs to have a 50% chance of one collision. For all practical purposes, every UUID v4 is unique.
UUID v1 is time-based using the MAC address and timestamp. UUID v3 uses MD5 hashing of a namespace and name. UUID v4 is randomly generated (this tool uses v4). UUID v5 uses SHA-1 hashing of a namespace and name. UUID v7 is a newer time-ordered format with random bits. Version 4 is the most commonly used in modern applications.
UUIDs work well as primary keys in distributed systems where coordination between databases is impractical. However, random UUID v4 values can cause B-tree index fragmentation. Consider time-ordered alternatives like UUID v7 or ULID if insert performance is critical.
Yes. Use the Format dropdown to select "Without Hyphens". The resulting 32-character hexadecimal string is still a valid UUID representation and can be converted back to the standard hyphenated format by inserting hyphens at positions 8, 12, 16, and 20.
This tool supports generating up to 100 UUIDs in a single batch. All are generated instantly in your browser using cryptographic randomness and displayed in a text area for easy copying.