Generate one or many random Version 4 UUIDs (universally unique identifiers) instantly, using your browser's secure random generator.
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A Universally Unique Identifier (UUID) is a 128-bit number usually written as a 36-character text string (divided into five groups separated by hyphens, such as `f47ac10b-58cc-4372-a567-0e02b2c3d479`), and it's widely used in software engineering to identify each database record, file, or user session with a unique identifier that practically never repeats, even without central coordination between different systems. This tool generates version 4 (v4) identifiers, the most common type, where all its random bits (except for a few fixed bits identifying the version and variant) are generated through a cryptographically secure random number generator (`crypto.getRandomValues`), making the probability of the same identifier repeating twice practically negligible. The specific fixed bits marking a UUID's version and variant are what allow software to recognize a v4 UUID reliably, distinguishing it from other UUID versions that generate their bits using different underlying methods entirely. Software can recognize a v4 UUID immediately by this fixed bit pattern, which is why the third group of digits in a v4 UUID always begins with 4, and the fourth always begins with 8, 9, a, or b.
Coordinating unique identifiers across multiple independent systems โ different servers, different databases, different applications that have never communicated with each other โ is a genuinely hard distributed-systems problem if approached through a central counter or registry. UUIDs solve this problem in a fundamentally different way: rather than coordinating centrally, each system simply generates its own identifier locally and relies on the sheer size of the number's possible range to make an accidental collision astronomically unlikely.
A UUID is a 128-bit number, giving roughly 340 undecillion (3.4 ร 10ยณโธ) possible distinct values. Version 4, the type generated by this tool, uses that enormous range almost entirely for randomness โ 122 of the 128 bits are generated randomly, with the remaining 6 bits fixed to specific values that identify the UUID as version 4 and mark it with the standard 'variant' bit pattern, which is exactly why a v4 UUID's third group of digits always begins with the digit 4, and its fourth group always begins with one of 8, 9, a, or b.
The practical consequence of this enormous random range is genuinely counterintuitive: even generating a billion UUIDs per second continuously would take on the order of 100 years before the probability of any two of them accidentally matching reached even a 50% chance โ a scenario so far outside realistic usage that UUID collisions are treated as a non-issue in virtually all real-world software design, despite technically being possible in principle.
Using a cryptographically secure random source for UUID generation, rather than an ordinary pseudo-random function, matters because the entire uniqueness guarantee depends on the randomness being genuinely unpredictable and evenly distributed across the full 122-bit range โ a weaker random source with subtle statistical biases could, in principle, make certain UUID values meaningfully more likely than others, quietly undermining the collision-avoidance guarantee the whole system depends on.
UUIDs are used throughout modern software wherever a unique identifier is needed without a central coordinating authority: primary keys for database records in distributed systems, unique filenames for uploaded files to avoid overwriting existing ones, session tokens for tracking a user's activity, and correlation identifiers for tracing a single request as it moves through multiple independent microservices in a larger application.
UUID version 4 means the identifier is generated almost entirely from random bits (rather than from a timestamp or hardware address like other UUID versions), which is why it's the most commonly used version for general-purpose unique IDs.
With 122 random bits, the number of possible v4 UUIDs is so astronomically large (over 5 undecillion) that the chance of ever generating a duplicate by accident is negligible for virtually any practical use.
This tool caps at 50 per click to keep the output easy to read and copy; if you need a much larger batch, you can simply click Generate multiple times and combine the results.