A UUID (Universally Unique Identifier) is a 128-bit identifier used to uniquely identify information in computer systems. UUIDs are standardized by RFC 4122 and are designed to be unique across time and space without requiring a central coordinating authority. They are commonly used in databases, APIs, distributed systems, and software applications where unique identifiers are required.

UUIDs are displayed as 32 hexadecimal digits, grouped into five sections separated by hyphens:550e8400-e29b-41d4-a716-446655440000. This format ensures readability while maintaining the identifier's uniqueness properties. UUIDs are particularly valuable in distributed systems where multiple servers or services need to generate unique identifiers independently without coordination.

The two most common UUID versions are v4 (random) and v1 (time-based). Each has distinct characteristics:

• UUID v4 (Random): Uses cryptographically strong random numbers. Provides no information about when or where it was created. Most commonly used version. Recommended for most applications due to privacy and security benefits. No risk of revealing system information.
• UUID v1 (Time-based): Includes a timestamp and MAC address. Sortable by creation time. Can reveal information about the generating machine. Useful when you need chronological ordering or when debugging distributed systems. If you need to work with Unix timestamps, check out our Unix Timestamp Converter.

For most modern applications, UUID v4 is the recommended choice. It provides better privacy (no information leakage), security (no predictable patterns), and is simpler to implement. Use UUID v1 only when you specifically need time-based ordering or when working with legacy systems that require it.

Choosing between UUIDs and auto-increment IDs depends on your application's requirements:

Modern applications often use UUIDs for primary keys in distributed systems and APIs, while auto-increment IDs remain popular for internal database relationships and performance-critical applications. Many systems use a hybrid approach: UUIDs for external-facing identifiers and auto-increment IDs for internal relationships. When working with APIs that return JSON data with UUID identifiers, you can use our JSON Viewer tool to inspect and validate the response structure.

• Database Primary Keys: Using UUIDs as primary keys allows for distributed ID generation and prevents conflicts when merging databases
• API Identifiers: UUIDs provide opaque identifiers that don't reveal internal system structure or sequential information
• Session Tokens: Generating unique session identifiers for user authentication and authorization
• File Identifiers: Creating unique identifiers for files in storage systems, especially in distributed file systems
• Event IDs: Tracking events in event-sourced systems where each event needs a unique identifier
• Microservices: Generating IDs independently across multiple services without coordination
• Data Synchronization: Merging data from multiple sources without ID conflicts
• Security: Using UUIDs to avoid exposing sequential patterns that could be exploited

All UUID generation happens entirely in your browser using JavaScript and crypto-safe random number generators. Your data never leaves your device, is never sent to any server, and is never stored. This privacy-first approach ensures that sensitive identifiers like database keys, API tokens, or session IDs remain completely private and secure. Whether you're generating UUIDs for development, testing, or production use, your data stays local and secure.