UUID v4 & v7 Generator, Bulk Output

A UUID, universally unique identifier, is a 128-bit value used as a unique ID across databases, distributed systems, and APIs without needing a central authority to hand out sequential numbers. Not every UUID is generated the same way, though, and the version matters more than most people realize once that ID becomes a primary key. This tool generates both the classic fully random v4 format and the newer, timestamp-ordered v7 format, in bulk, entirely in your browser.

UUID v4: fully random, no order

Version 4 is the UUID format most people are already familiar with. Per RFC 4122, 122 of its 128 bits are randomly generated, with a small number of fixed bits identifying the version and variant. This makes v4 IDs statistically unique for all practical purposes, the odds of a collision are vanishingly small, but it also means two v4 UUIDs generated back to back have no relationship to each other whatsoever. There is no way to tell which was created first just by looking at the value, which is exactly the behavior you want for something like a session token or a random resource identifier where order should never leak information.

UUID v7: sortable, timestamp-based

Version 7 takes a different approach, defined more recently to solve a real, common problem with using v4 as a database primary key. A v7 UUID embeds a 48-bit Unix millisecond timestamp in its most significant bits, followed by random bits for the remainder. The result is a UUID that is still effectively unique and still contains enough randomness to be unpredictable, but that also sorts chronologically when ordered as plain values, since the timestamp portion dominates the ordering. Generate a batch of v7 UUIDs a second apart and sort them as strings, they come out in the same order they were created.

Why this matters for database performance

This distinction is not just theoretical. Many relational databases store primary key indexes as B-trees, which perform best when new values are inserted in roughly ascending order, appended to the end of the index. A fully random v4 UUID, when used as a primary key, forces the database to insert new rows at random positions throughout the index rather than at the end, leading to index fragmentation and measurably worse write performance at scale. A v7 UUID, because it is naturally ascending over time, avoids this problem while still offering a globally unique, non-sequential, hard to guess identifier, which is exactly why it has seen growing adoption specifically as a primary key replacement for v4 in newer database schemas.

Bulk generation, and controlling the output format

Beyond generating a single ID, this tool supports bulk output, up to 1000 UUIDs in a single batch, useful for seeding test data, pre-generating a pool of identifiers, or populating a fixture file. Formatting options let you toggle hyphens on or off, since some systems expect the standard hyphenated format while others store UUIDs as a flat 32 character hex string, and toggle uppercase, since a small number of legacy systems expect uppercase hex digits rather than the RFC's default lowercase.

Cryptographically secure, and fully local

Every UUID generated here uses your browser's Web Crypto API, specifically crypto.randomUUID and crypto.getRandomValues, a cryptographically secure random number source, not a weaker pseudo-random generator like Math.random. Generation happens entirely client side, nothing is sent to a server, logged, or stored, so a batch generated here is exactly as private as one generated by a local script. If you need a different kind of unique, human memorable identifier rather than a UUID, our Password & Passphrase Generator uses the same secure random source for a different purpose, part of the same Developer Utilities collection this tool belongs to.