UUID Generator for v4 and v7 with Bulk Output

What is a UUID?

A UUID (Universally Unique Identifier) is a 128-bit value written as 32 hexadecimal digits in five hyphenated groups: 8-4-4-4-12, for example 3d609887-76b3-4fd4-b371-49e10ee830a7. The format is defined by RFC 9562, which replaced RFC 4122 in 2024. Because a UUID can be generated anywhere without asking a central server for the next number, it is the standard way to give database rows, API resources, files, messages and idempotency keys an ID before they are ever saved.

Two fields inside the value describe how it was made. The first digit of the third group is the version (the 4 in 4fd4), and the first digit of the fourth group encodes the variant (8, 9, a or b for RFC 9562 UUIDs). The inspector on this page reads both, so you can paste any ID from a log or a database and see what produced it.

UUID v4 vs v7, and why v7 is better for database primary keys

Version 4 is 122 bits of randomness. It is the default almost everywhere, and the chance of two v4 values colliding is negligible: you would need to generate around 2.7 quintillion of them for a 50% chance of a single duplicate. Its weakness is that random values land all over a B-tree index, so inserting millions of v4 primary keys into PostgreSQL, MySQL (InnoDB clusters rows by primary key) or SQL Server causes page splits, poor cache locality and index bloat.

Version 7 fixes that. Its first 48 bits are the Unix timestamp in milliseconds, followed by the version, a counter and random bits. New IDs therefore sort after older ones, inserts append to the end of the index like an auto-increment integer would, and you can still generate them on any machine without coordination. This generator also uses the 12-bit rand_a field as a counter within the same millisecond (RFC 9562 method 1), so a bulk batch stays in creation order. The trade-off: a v7 UUID reveals when it was created, so do not use it where the creation time is sensitive. For public, unguessable tokens prefer v4 or a dedicated random token.

GUID vs UUID

A GUID (Globally Unique Identifier) is Microsoft's name for the same 128-bit identifier, and in practice the two terms are interchangeable. What differs is presentation: Windows tools, the registry and .NET often print GUIDs in uppercase and wrapped in braces, such as {3D609887-76B3-4FD4-B371-49E10EE830A7}. Tick Uppercase and Braces above to produce that format. One real difference to know about: .NET's Guid.ToByteArray() and SQL Server store the first three groups little-endian, so the raw bytes of a GUID differ from the RFC byte order even though the text form is identical.

Generate a UUID in Python, JavaScript, SQL Server and PostgreSQL

Python: import uuid; uuid.uuid4() returns a random UUID, and str(uuid.uuid4()) gives the hyphenated text. Python 3.14 adds uuid.uuid7().

JavaScript: crypto.randomUUID() is built into every modern browser and Node.js 19+ (also available as require('node:crypto').randomUUID() in Node 14.17+). It returns a lowercase v4 string. For v7 in Node, the uuid package exposes v7().

SQL Server: SELECT NEWID(); returns a random UNIQUEIDENTIFIER. NEWSEQUENTIALID() is only allowed as a column default and gives sequential values that sort by SQL Server's own byte order rather than RFC 9562 v7.

PostgreSQL: SELECT gen_random_uuid(); is built in from version 13 (earlier versions need the pgcrypto extension). PostgreSQL 18 adds uuidv7() for time-ordered keys.

This page uses the same primitive as the JavaScript example: crypto.randomUUID() for v4, with a crypto.getRandomValues() fallback, and getRandomValues() plus the current time for v7.