UUID Generator

A UUID (Universally Unique Identifier) is a 128-bit integer which is represented by a 36 character string, uniquely identifying information. The format is 8-4-4-4-12 bits, with each section holding different bits. How these bits are generated differs depending on the version, either by timestamp and network address, or by using a cryptographic random number generator.

UUIDs have an astronomically low probability of collision. The probability of generating a duplicate is about 1 in 5.3 × 10³⁶ for v4 UUIDs generated using cryptographically secure random numbers. For comparison, if you were creating 1 billion UUIDs every second, you would only have a chance of collision after running for approximately 100 billion years. In reality, UUIDs have been used in any application as unique.

UUID v7 is recommended for most modern applications. It offers time-ordered values (useful for database indexes), generates fast without external dependencies, and doesn’t reveal sensitive information such as MAC addresses. If you’re using PostgreSQL, it has native support for uuid-ossp extension including v7. For legacy systems or certain compatibility requirements, ordering can be matched to v1, but is enhanced with improved field layout in v6.

Modern browsers and libraries such as Bouncy-cast e.g. use UUID v4 to generate cryptographically random numbers. Although it is possible in theory if the attacker knows exactly how the random number generator works, it is not possible in practice because the 122 bits of randomness make it completely impractical to guess the result. But don’t use UUIDs as cryptographic tokens, session IDs for high-security applications or anything that really needs randomness (use Web Crypto API).

Technically, nothing. Microsoft’s implementation of the UUID standard is called GUID. UUID is internationally recognized as per RFC 4122, and GUID is commonly used in a Microsoft environment. Both are 128-bit identifiers of the same structure and function. The “GUID” versus “UUID” seems to be a matter of terminology.

The hyphens in a UUID are only there to make it easier to read by humans, to make logical sense, and to separate the 128 bits into chunks as time_low (8 hex), time_mid (4 hex), time_hi_and_version (4 hex), clock_seq (4 hex), and node (12 hex). Both formats are valid and equal. Always use the hyphenated format for displays to humans – the compact format for URLs, files, or database storage where space is important.

A valid UUID consists of 8 hex digits followed by a hyphen, 4 hex digits, a hyphen, 4 hex digits, a hyphen, 4 hex digits, a hyphen, 12 hex digits (total of 36 characters including hyphens). The regex pattern is: ^[0-9a-f]{8}-[0-9a-f]{4}-[0-9a-f]{4}-[0-9a-f]{4}-[0-9a-f]{12}$</. Also, the version digit (13th character) must be 1, 3, 4, 5, 6 or 7 and the variant digit (17th character) must be 8, 9, a, or b.

Absolutely. This uuid generator is a 100% browser based, JavaScript implementation. No UUIDs are ever sent to a server or stored anywhere other than in your local browser. Your generated UUIDs are only stored in your browser’s memory, and optionally in local storage for history purposes. This can be done offline (on the first page loading, generation takes place without the presence of the internet).