UUID / GUID Generator
Click generate to create a random v4 UUID, or specify how many you need (up to 100) for batch generation.
Reviewed by the ToolNestr Editorial Team — July 2026
crypto.randomUUID() or crypto.getRandomValues().
How UUID generation works
UUID v4 (random) generation uses a cryptographically secure random number generator to produce 122 bits of randomness, combined with 6 fixed bits for version and variant identification. The 128-bit total is formatted according to RFC 4122 as an 8-4-4-4-12 hexadecimal string with hyphens, creating a standard 36-character identifier.
The random bits are generated using crypto.getRandomValues() on the browser, which draws entropy from the operating system's secure random source. With 122 random bits, there are 5.3 × 10³⁶ possible UUIDs — the probability of collision is astronomically low, making them safe for distributed systems without central coordination.
Worked example
What different UUID versions mean
Each UUID version uses a different strategy for generating unique identifiers. Here is how they compare.
Developer
Generates UUIDs for database primary keys, API resource identifiers, and distributed system tracing IDs.
Database Administrator
Uses UUIDs for replication-safe primary keys across distributed databases and conflict-free merge replication.
System Architect
Designs microservice systems using UUIDs for event correlation, request tracing, and service-to-service message identification.
Project Manager
Generates unique reference IDs for tasks, tickets, and documentation to ensure unambiguous identification across teams.
| Version | Method | Use Case |
|---|---|---|
| v1 | Timestamp + MAC address | Time-ordered IDs, legacy systems |
| v3 | MD5 hash of namespace + name | Deterministic IDs from names |
| v4 | Random bytes | General-purpose, most common |
| v5 | SHA-1 hash of namespace + name | Deterministic IDs, better than v3 |
| v7 | Unix timestamp + random | Time-ordered DB keys |
How to use UUID Generator
Set the quantity
Enter how many UUIDs you need, from 1 to 100. For bulk operations like seeding a database, set a higher number.
Click Generate
Click the Generate button to create UUIDs using your browser's cryptographically secure random generator.
Copy individually or all
Click the copy icon on any single UUID, or use "Copy All" to grab every generated UUID in one go.
Tips for using UUIDs
Use v4 for general-purpose IDs
UUID v4 (random) is the most widely supported and secure choice for most applications. It requires no coordination between systems and provides excellent randomness.
Consider DB index performance
Random UUIDs can cause B-tree index fragmentation in databases. For large tables with UUID primary keys, consider UUID v7 or ULIDs which are time-ordered and more cache-friendly.
Use deterministic UUIDs when needed
If you need the same input to always produce the same UUID, use v3 or v5. These are useful for generating consistent IDs from resource names or URLs.
What are UUIDs?
UUIDs (Universally Unique Identifiers) are 128-bit identifiers standardized as RFC 4122. They provide a way to generate unique identifiers without requiring a central registration authority. The 128 bits are divided into fields that encode version information, variant information, and the unique identifier itself. UUIDs are commonly displayed as 36-character hexadecimal strings in the format 8-4-4-4-12.
The total number of possible v4 UUIDs is 2^122 (approximately 5.3 × 10^36), making collisions astronomically unlikely. To put this in perspective, you would need to generate 1 billion UUIDs per second for 100 years to have a 50% chance of a single collision. This makes UUIDs suitable for massive distributed systems.
UUID Format
A UUID is a 36-character string formatted as 8-4-4-4-12: 8 hexadecimal digits, a hyphen, then three groups of 4 hexadecimal digits separated by hyphens, followed by 12 hexadecimal digits. For example: 550e8400-e29b-41d4-a716-446655440000. The hyphens are part of the standard representation but are not always required in storage.
The format encodes metadata about the UUID. The 13th character (the first digit of the third group) represents the version number (e.g., "4" for v4). The 17th character represents the variant. This allows software to parse and understand any UUID without additional context about how it was generated.
UUID Version Differences
UUID v1 uses the current timestamp and the host's MAC address to generate IDs. This makes v1 UUIDs time-ordered and predictable on the same machine, but the MAC address raises privacy concerns. v4 uses random bytes exclusively and is the most popular version due to its simplicity and security properties.
v3 and v5 are deterministic name-based UUIDs. They take a namespace UUID and a name string, hash them together (MD5 for v3, SHA-1 for v5), and produce a fixed UUID. This means the same name in the same namespace always produces the same UUID, which is useful for generating consistent identifiers from URLs, DNS names, or object IDs.
UUID Use Cases
UUIDs are everywhere in modern software. They serve as database primary keys (especially in distributed databases), API resource identifiers, session tokens, event correlation IDs in microservices, and transaction identifiers in payment systems. Their key advantage is that any system can generate them independently without coordination.
In distributed systems, UUIDs eliminate the bottleneck of centralized ID generation. Each service, database node, or client can generate unique IDs without contacting a central authority. This makes them ideal for offline-capable applications, conflict-free replicated data types, and multi-region database deployments where network latency makes sequential IDs impractical.
Frequently asked questions
What is a UUID?
A UUID (Universally Unique Identifier) is a 128-bit identifier standardized by RFC 4122. It is designed to be unique across space and time without requiring a central registration authority.
What is the difference between UUID and GUID?
GUID (Globally Unique Identifier) is Microsoft's implementation of the UUID standard. The terms are often used interchangeably, with GUID being more common in Windows ecosystems.
What is UUID v4?
UUID v4 is a randomly generated UUID where 122 of the 128 bits come from a cryptographically secure random number generator. The remaining 6 bits are used for version and variant identification.
What is the UUID format?
UUIDs are 36-character strings in the format 8-4-4-4-12: 8 hex digits, a hyphen, 4 hex digits, a hyphen, 4 hex digits, a hyphen, 4 hex digits, a hyphen, and 12 hex digits.
Can two UUIDs ever be the same?
The probability of a collision with v4 UUIDs is extremely small. With 2^122 possible values, you would need to generate billions per second for centuries to have a significant chance of collision.
What are UUIDs used for?
UUIDs are used as database primary keys, API resource identifiers, session identifiers, event tracking IDs, and anywhere globally unique identifiers are needed without a central authority.
What are the different UUID versions?
There are five versions: v1 (time-based), v2 (DCE security), v3 (name-based with MD5), v4 (random), and v5 (name-based with SHA-1). v4 is the most commonly used.
Is my data private when using this tool?
Yes. UUIDs are generated using crypto.randomUUID() or crypto.getRandomValues() built into your browser. No data is sent to any server.
What is the difference between UUID v4 and UUID v7?
UUID v7 is a newer draft standard that combines a Unix timestamp with random bits. It provides time-ordered UUIDs that are more efficient as database primary keys. v4 remains the most widely supported version.
Can I use UUIDs as database primary keys?
Yes, but be aware of performance implications. UUIDs are 128-bit (16 bytes), larger than auto-increment integers (4 bytes). They can cause index fragmentation in MySQL. UUID v7 or ULID are better alternatives for database use.