UUID Generator

Generate UUID/GUID online instantly. Create UUID v4 and v1 with bulk generation support.

UUID v4 (Random)

UUID v1 (Timestamp)

Bulk Generate

What is UUID?

UUID (Universally Unique Identifier), also known as GUID (Globally Unique Identifier), is a 128-bit standardized identifier used extensively in software development and distributed computing systems. First introduced in the Apollo Network Computing System (NCS) in the 1980s and later standardized by the Open Software Foundation (OSF) as part of the Distributed Computing Environment (DCE), UUID has become an essential component of modern software architecture. The current specification is defined in RFC 4122 by the Internet Engineering Task Force (IETF).

History and Origin of UUID

The concept of UUID originated in the early 1980s at Apollo Computer for their Network Computing System. The goal was to create identifiers that could be generated independently across different systems without requiring central coordination or synchronization. This revolutionary approach allowed distributed systems to generate unique identifiers locally while maintaining global uniqueness. The technology was later adopted by the Open Software Foundation and incorporated into the Distributed Computing Environment in 1990. In 2005, RFC 4122 formalized the UUID specification, establishing the standard format and generation algorithms used today. UUIDs are now ubiquitous in modern computing, from database systems and web services to mobile applications and cloud infrastructure.

UUID Structure and Format

A UUID consists of 32 hexadecimal digits displayed in five groups separated by hyphens, following the pattern 8-4-4-4-12 (e.g., 550e8400-e29b-41d4-a716-446655440000). The 128-bit value is typically represented as a lowercase string of 36 characters including hyphens. The structure includes variant and version bits that indicate the UUID type and generation method. The variant field determines the layout of the UUID, with most modern UUIDs using RFC 4122 variant. The version field (4 bits) identifies the generation algorithm: version 1 (timestamp-based), version 3 (MD5 hash), version 4 (random), version 5 (SHA-1 hash), with version 4 being most commonly used in contemporary applications.

Why Use UUID Generator?

  • ✓Free to use with unlimited generation
  • ✓Instant UUID generation
  • ✓Support UUID v1 and v4
  • ✓Bulk generation for multiple UUIDs
  • ✓One-click copy to clipboard
  • ✓Generated locally in your browser

UUID Versions

UUID v4 (Random-based)

Version 4 UUIDs are generated using cryptographically strong pseudo-random numbers. This is the most widely adopted version in modern applications due to its simplicity and excellent uniqueness properties. With 122 random bits, the probability of collision is approximately 1 in 2^122 (5.3 x 10^36), making it statistically impossible to generate duplicates in any practical scenario. V4 UUIDs are ideal for distributed systems where coordination between nodes is impractical or impossible. Major platforms including Java's java.util.UUID, Python's uuid module, and JavaScript's crypto.randomUUID() default to version 4 generation.

UUID v1 (Timestamp-based)

Version 1 UUIDs incorporate the current timestamp (60-bit count of 100-nanosecond intervals since October 15, 1582) and the MAC address of the generating machine. This ensures uniqueness across both time and space. The timestamp component allows UUIDs to be sorted chronologically, which can improve database index performance. However, V1 UUIDs have privacy implications as they expose the generating machine's MAC address and creation time. They're commonly used in scenarios requiring time-ordered identifiers, such as event logging, time-series databases, and systems where chronological sorting is beneficial. Modern implementations may use random node IDs instead of MAC addresses to address privacy concerns.

UUID Performance and Efficiency

UUID generation is computationally inexpensive and can produce millions of identifiers per second on modern hardware. Version 4 generation typically requires only a cryptographic random number generator call, while version 1 needs timestamp and node ID retrieval. In database systems, UUIDs as primary keys offer excellent scalability for distributed databases and multi-master replication scenarios, eliminating the need for centralized ID generation. However, they're larger than auto-increment integers (128 bits vs 32-64 bits), which can impact storage and index performance. The random nature of V4 UUIDs can cause B-tree index fragmentation in traditional relational databases, though this is mitigated in modern database engines with UUID-optimized storage. Sequential UUIDs or ordered UUID variants (like ULID or UUID v6/v7) address this limitation while maintaining uniqueness guarantees.

Security Considerations

UUID v4 generation relies on cryptographically secure random number generators (CSPRNG) to ensure unpredictability, making them suitable for security-sensitive applications like session tokens, API keys, and password reset tokens. The astronomical entropy (2^122 possible combinations) makes brute-force attacks computationally infeasible. However, developers should note that UUIDs are not designed as secrets - they're identifiers, not authentication credentials. Version 1 UUIDs should be avoided in security contexts as they're partially predictable and leak information about generation time and hardware. For security-critical applications requiring both uniqueness and unpredictability, UUID v4 combined with proper access controls and encryption provides robust identifier management. All UUID generation on this tool occurs entirely within your browser using the Web Crypto API, ensuring your identifiers are never transmitted to external servers.

How to Use

  1. Choose UUID version (v1 or v4)
  2. Click Generate button
  3. Copy the generated UUID
  4. For bulk generation, select quantity and generate

Common Use Cases

  • Database Primary Keys: Use UUIDs as unique identifiers
  • API Identifiers: Generate unique IDs for API resources
  • Session IDs: Create unique session identifiers
  • File Names: Generate unique file names
  • Distributed Systems: Ensure uniqueness across systems

Frequently Asked Questions

What is the difference between UUID v1 and v4?

UUID v1 generates identifiers based on timestamp (60-bit time value) and MAC address, ensuring uniqueness across time and space. The timestamp allows chronological sorting, but exposes generation time and hardware information. UUID v4 uses cryptographically strong random numbers (122 random bits) for generation, providing better privacy and unpredictability. V4 is stateless and simpler to implement, making it the preferred choice for 95% of modern applications including web services, microservices, and cloud applications.

Are UUIDs truly unique?

Yes, UUIDs provide practical uniqueness guarantees. For UUID v4, with 122 random bits, the probability of generating a duplicate is approximately 1 in 5.3 × 10^36. To put this in perspective, generating one billion UUIDs per second for 100 years would produce a collision probability of only 0.0000000000005%. UUID v1 guarantees uniqueness through timestamp precision (100-nanosecond intervals) and machine identification. While theoretically possible for collisions to occur in v4, it's statistically impossible in any real-world scenario. Major tech companies generate billions of UUIDs daily without collision issues.

Can I use UUID as a primary key in databases?

Yes, UUIDs are excellent primary keys for distributed databases and modern applications. Benefits include: (1) Client-side generation without database round-trips, (2) Merge-friendly for multi-master replication, (3) No sequential prediction vulnerability, (4) Globally unique across all tables and databases. Considerations: UUIDs are larger than integers (16 bytes vs 4-8 bytes), which increases storage and index size. Random UUIDs can cause index fragmentation in B-tree indexes. Modern solutions include UUID v6/v7 for time-ordered UUIDs, or database-specific optimizations (PostgreSQL's UUID type, MySQL's UUID_TO_BIN()). Major platforms like MongoDB, Cassandra, and DynamoDB use UUID-like identifiers as default.

How long is a UUID and what's the format?

A UUID is exactly 128 bits (16 bytes) in length. The canonical textual representation is 36 characters: 32 hexadecimal digits (0-9, a-f) plus 4 hyphens in the format 8-4-4-4-12 (example: 550e8400-e29b-41d4-a716-446655440000). The string representation uses 36 bytes of storage, while binary storage uses 16 bytes. The five groups represent: (1) time_low (8 hex digits), (2) time_mid (4 hex digits), (3) time_hi_and_version (4 hex digits), (4) clock_seq_and_reserved (4 hex digits), and (5) node (12 hex digits). Some systems use alternative representations like Base64 encoding (22 characters) for more compact URLs.

Is UUID generation secure and private?

UUID v4 generation is cryptographically secure when using proper random number generators. Our tool uses the Web Crypto API (crypto.getRandomValues()) which provides cryptographically strong random numbers suitable for security-sensitive applications. All generation occurs entirely in your browser - no data is sent to servers, ensuring complete privacy. However, important notes: (1) UUIDs are identifiers, not secrets or passwords - they can be exposed safely in URLs and APIs, (2) UUID v1 exposes timestamp and potentially MAC address, reducing privacy, (3) For authentication tokens, combine UUIDs with proper access controls and expiration, (4) UUIDs alone don't provide authentication - they must be validated server-side. For maximum security: use v4, generate server-side for tokens, implement rate limiting, and never use UUIDs as sole authentication mechanism.

What are the advantages of UUID over auto-increment IDs?

UUIDs offer several advantages: (1) Global uniqueness without coordination - can be generated independently across distributed systems, (2) No database round-trip required for ID generation, improving performance, (3) Merge-friendly for database replication and sharding, (4) Security - non-sequential nature prevents enumeration attacks, (5) Offline capability - IDs can be generated without database connection, (6) Flexibility - same ID space can be used across multiple tables and databases. Trade-offs include larger storage size, potential index fragmentation, and less human-readable format. Best for: microservices, distributed systems, public APIs, offline-first applications. Use auto-increment for: single-database systems, chronologically ordered data, storage-constrained environments.

How many UUIDs can be generated before collision?

For UUID v4 with 122 random bits, you can generate approximately 2.71 × 10^18 (2.71 quintillion) UUIDs before reaching a 50% probability of a single collision. To illustrate the scale: generating 1 trillion (10^12) UUIDs results in collision probability of only 0.0000000000005%. Even if every person on Earth generated 1 million UUIDs per second for an entire year, collision probability would remain negligible. The birthday paradox applies, but the enormous key space makes collisions statistically impossible for any practical application. UUID v1 has even stronger guarantees through timestamp precision - two UUIDs generated on different machines or at different times (>100 nanoseconds apart) are guaranteed unique.

Which UUID version should I choose?

Choose UUID v4 for 95% of use cases: web applications, APIs, microservices, session IDs, resource identifiers. It's simple, secure, and provides excellent uniqueness. Use UUID v1 when: (1) chronological sorting is important, (2) you need to extract timestamp from IDs, (3) database index performance with time-ordering is critical. Avoid v1 if privacy is a concern (exposes MAC address). Emerging alternatives: UUID v6 (time-ordered like v1 but improved), UUID v7 (Unix timestamp-based, better database performance), ULID (lexicographically sortable, URL-safe). For new projects in 2025, consider v4 for general use, v7 for database-heavy applications requiring time-ordering, or ULID for better human-readability and sorting.

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