UUID generator for v4 and v7

What is a UUID?

A UUID, or universally unique identifier, is a 128-bit value used to label data without a central registry. Version 4 fills 122 bits with secure random data, so two matching IDs are very unlikely. Version 7 puts a Unix timestamp in milliseconds at the front, so IDs sort by when they were made. That makes v7 a good fit for primary keys.

Generate UUIDs in bulk

Need seed data or test fixtures? Set the count up to 1,000, turn on uppercase or turn off hyphens, and copy the whole list with one click. Every ID is made in this browser tab and nothing is sent to a server.

UUID v7 explained

UUID version 7 is defined in RFC 9562, published in May 2024. That RFC replaces the original RFC 4122 and also covers versions 1 to 6 and 8. A v7 UUID starts with a 48-bit big-endian Unix timestamp in milliseconds. Then come the 4-bit version number, which is 7, 12 random bits, the 2-bit variant and 62 more random bits. Because the timestamp comes first, v7 UUIDs sort by creation time both as bytes and as text. The 74 random bits keep them unique across machines with no coordination.

Why UUID v7 is better for database keys

Most databases store primary keys in a B-tree index. Random v4 values land anywhere in that index, so each insert can touch a different page. That causes page splits and poor cache use as the table grows. v7 values arrive in roughly increasing order, so new rows go near the end of the index, much like an auto-increment integer. You still get IDs you can create anywhere: in the client, across services, or before the row is written. Time-ordered keys also make cursor pagination and "newest first" queries simpler.

Should you use UUID v4 or v7?

Use v4 when you need an ID that can't be guessed and has no order, or when the ID shouldn't reveal when it was made. Use v7 for database keys and event logs, where time order helps the index and pagination. Both are standard. Any system with a UUID column accepts either version.

How to tell a v4 from a v7 UUID

The version is written into the UUID, so you can check it by eye:

• Look at the first character of the third group. 4 means version 4, and 7 means version 7.
• The first character of the fourth group is 8, 9, a or b for both. That's the RFC variant.
• In a v7 UUID, the first 12 hex digits, which are the first group plus the second, hold the creation time. Convert them from hex to decimal to get Unix milliseconds.

Before you start

UUID Generator works on the text or values you enter. Output: UUIDs. The settings appear before anything runs, so you can check them first. Your original file is never changed.

The value you enter is processed in your browser. Still test the output where it will be used. Clean formatting does not prove the data is safe or correct.

Keep the original until you have opened and checked the result. The work happens in this browser tab, so the size you can handle depends on your device's memory, your browser and the file itself.

How to use the UUID generator for v4 and v7

1. Choose UUID version 4, which is random, or version 7, which is time-ordered.
2. Set how many UUIDs you need and adjust casing or hyphens.
3. Click Regenerate to get a fresh batch.
4. Copy all UUIDs to your clipboard.