What is a UUID?
A UUID (Universally Unique Identifier), also known as GUID (Globally Unique Identifier) in Microsoft systems, is a 128-bit identifier that is designed to be unique across all devices and time. The standard representation is a 36-character string consisting of 32 hexadecimal digits displayed in five groups separated by hyphens: xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx.
UUIDs are fundamental to modern software development, providing a reliable way to identify resources without requiring coordination between systems. Unlike sequential IDs that require a central authority, UUIDs can be generated independently on any device with extremely low collision probability.
UUID Versions Explained
UUID Version 1 (Time-based)
UUID v1 generates identifiers based on the current timestamp and the MAC address of the generating machine. This version provides temporal sequencing, meaning you can extract when a UUID was created. However, it also exposes information about the generating host, which may be a privacy concern in some applications.
The structure includes the current timestamp (100-nanosecond intervals since October 15, 1582), a clock sequence to handle timestamp collisions, and a node identifier (typically derived from the MAC address).
UUID Version 4 (Random)
UUID v4 is the most commonly used version. It generates identifiers using cryptographically secure random numbers. With approximately 5.3 × 10^36 possible values, the probability of collision is negligible for practical purposes—you would need to generate approximately 2.71 quintillion random UUIDs to have a 50% chance of a single collision.
This version is ideal for most applications because it doesn’t expose any information about the generating system and doesn’t require synchronized clocks.
UUID Version 5 (Name-based)
UUID v5 generates deterministic identifiers by hashing a namespace UUID with a name using SHA-1. Given the same namespace and name, the same UUID will always be generated. This is useful for creating consistent identifiers from meaningful inputs.
Standard namespaces include DNS (for domain names), URL (for URLs), OID (for ISO Object Identifiers), and X.500 DNs. You can also define custom namespaces for application-specific use cases.
UUID vs GUID
While technically the same concept, UUID is the term used in the open standards (RFC 4122), while GUID is Microsoft’s terminology. Both refer to 128-bit identifiers with the same structure. The main practical difference is formatting conventions—Microsoft tools often display GUIDs in uppercase with braces.
How to Use This Tool
Generating UUIDs: Select your preferred version (v1, v4, or v5), choose an output format, set the quantity (1-100), and click Generate. For UUID v5, you’ll also need to select a namespace and provide a name.
Validating UUIDs: Switch to the Validate tab, paste any UUID string, and the tool will tell you if it’s valid, what version it is, and extract relevant metadata like timestamps for v1 UUIDs.
Formatting Options: Choose from Standard (lowercase with dashes), Uppercase, No Dashes (“nodashes”), Braces (Microsoft GUID format), or URN format.
Common Use Cases
Database Primary Keys
UUIDs make excellent primary keys, especially in distributed databases where auto-incrementing integers would require coordination. They enable merging data from multiple sources without key conflicts.
Distributed Systems
In microservices architectures, UUIDs allow each service to generate unique identifiers independently without a centralized ID service. This improves scalability and reduces single points of failure.
Session and Token Identifiers
UUIDs are ideal for session IDs, API tokens, and correlation IDs. Their unpredictability (especially v4) makes them suitable for security-sensitive identifiers.
File and Resource Naming
When you need unique filenames that won’t conflict, UUIDs provide a reliable solution. They’re commonly used for uploaded files, temporary files, and cached resources.
Content Addressing
UUID v5 can generate consistent identifiers for content based on its characteristics. This is useful for content-addressable storage and deduplication systems.
UUID Best Practices
Choose the right version: Use v4 for general purposes, v1 when you need temporal ordering, and v5 when you need deterministic generation from meaningful inputs.
Don’t rely on security through obscurity: While UUIDs are hard to guess, they shouldn’t be the sole security mechanism. Always implement proper authentication and authorization.
Consider database performance: Some databases perform better with sequential UUIDs (like v1) or specially optimized UUID types. PostgreSQL’s uuid type and MySQL’s binary(16) are optimized for UUID storage.
Store efficiently: Store UUIDs as binary (16 bytes) rather than strings (36 characters) when possible to save space and improve query performance.
Technical Details
UUIDs follow the RFC 4122 specification. The 128 bits are organized as follows:
- time_low: 32 bits
- time_mid: 16 bits
- time_hi_and_version: 16 bits (4 bits for version)
- clock_seq_hi_and_reserved: 8 bits (contains variant)
- clock_seq_low: 8 bits
- node: 48 bits
The version number is encoded in bits 12-15 of the time_hi_and_version field, while the variant is encoded in the most significant bits of clock_seq_hi_and_reserved.
Privacy and Security
All UUID generation happens entirely in your browser using the Web Crypto API for secure random number generation. No data is transmitted to any server. You can verify this by checking your browser’s network tab while using the tool.
For UUID v1, our implementation uses a random node ID rather than your actual MAC address to protect your privacy while maintaining format compliance.
Frequently Asked Questions
Are UUIDs guaranteed to be unique?
For practical purposes, yes. The probability of collision with v4 UUIDs is approximately 10^-37 when generating one UUID per second for over 100 years. However, they’re not cryptographically guaranteed unique like some claim.
Which UUID version should I use?
UUID v4 is the safest default choice. Use v1 if you need temporal ordering, and v5 if you need deterministic generation from inputs like URLs or domain names.
Can I use UUIDs as passwords or secret keys?
No. While UUIDs are hard to guess, they’re identifiers, not secrets. Their format is predictable, and some versions expose information. Use proper cryptographic key generation for secrets.
Why do some UUIDs have uppercase letters?
Both cases are valid. RFC 4122 specifies lowercase for output, but parsing should be case-insensitive. Microsoft’s GUID format traditionally uses uppercase.
How do I store UUIDs efficiently in a database?
Store as binary(16) or use your database’s native UUID type. This saves space compared to varchar(36) and improves indexing performance.
Start Generating UUIDs
Use the tool above to generate unique identifiers for your projects. Whether you need a single UUID or hundreds, all generation happens instantly in your browser without any data leaving your device.