UUID v4 Generator
The UUID v4 generator creates cryptographically random universally unique identifiers using the browser's crypto.getRandomValues() API. Generate one or up to 20 UUIDs at once and copy any of them to clipboard. Free, instant, no account required.
How to generate a UUID online
Click Generate to produce one UUID v4. Set the quantity field to generate multiple UUIDs at once, up to 20 in a single generation. Each UUID appears as a lowercase hyphenated string in the standard 8-4-4-4-12 format: xxxxxxxx-xxxx-4xxx-yxxx-xxxxxxxxxxxx. The "4" in position 13 indicates version 4. The "y" value is one of 8, 9, a, or b, indicating the RFC 4122 variant. Click the copy icon next to any UUID to copy it to your clipboard.
Generate uuid online for immediate use in database records, API keys, session tokens, and any system that requires a unique identifier without a centralized authority to coordinate assignment. UUID v4 generation requires no network request, no database check, and no prior knowledge of existing identifiers. The probability of collision between two independently generated v4 UUIDs is 1 in 5.3 × 10^36, making duplicate generation for practical purposes impossible.
UUID v4 generator free: what makes v4 UUIDs unique
UUID v4 generator free relies on randomness rather than host identifiers or timestamps to ensure uniqueness. A version 4 UUID has 122 bits of randomness, 128 total bits minus 6 bits reserved for version and variant indicators. With 122 bits of random data, the keyspace contains 5.3 × 10^36 possible UUIDs. Even generating one billion UUIDs per second for a trillion years, the probability of generating a collision remains negligibly small.
The cryptographic random source used in this generator, crypto.getRandomValues(), produces values that pass the NIST SP 800-22 suite of statistical randomness tests. This distinguishes it from Math.random()-based UUID generators, which use a pseudo-random number generator with a shorter period that can theoretically produce repeating sequences. For production database keys, session identifiers, and API tokens, a cryptographically random UUID v4 generator free from predictability is appropriate.
Frequently asked questions
UUID stands for Universally Unique Identifier. It is a 128-bit identifier formatted as a 36-character hyphenated hexadecimal string. UUIDs are used as primary keys in databases to avoid sequential integer enumeration, as session tokens in web applications, as API keys and client identifiers, as correlation IDs for distributed system tracing, and as filenames for uploaded files to prevent collisions without a central counter.
UUID v1 is generated from the host MAC address and current timestamp, making it traceable to the machine and time of generation, a privacy concern. UUID v4 is generated from cryptographically random bits with no connection to any device or time, making it appropriate for most applications. UUID v5 is generated deterministically from a namespace and a name using SHA-1 hashing, producing the same UUID every time for the same input pair, useful for content-based addressing.
Yes. Set the quantity field to any number from 1 to 20 and click Generate. All UUIDs are generated simultaneously from the cryptographic random source and displayed in a list. Each one has its own copy button. This is useful for seeding test databases, generating batches of API tokens, or pre-generating identifiers for an import script.
In theory, yes, any finite random keyspace can produce a collision. In practice, a UUID v4 keyspace of 2^122 values makes collision probability negligible. Generating one billion UUIDs per second would require approximately 85 billion years before a 50 percent probability of collision is reached. For all practical engineering purposes, UUID v4 values can be treated as globally unique without any coordination mechanism.