UUID Generator (v4 & v7)
Updated Free mock REST & WebSocket APIs
Generate cryptographically random UUID v4s or time-ordered UUID v7s — one at a time or up to 1,000 in bulk. They're created in your browser with the Web Crypto secure random number generator.
Inspect a UUID (version, variant, embedded time)
🔒 Generated in your browser with the Web Crypto secure random generator — nothing is sent or stored.
How to generate UUIDs
- Choose v4 (random) or v7 (time-ordered).
- Enter how many you need (1–1,000) and click Generate.
- Pick uppercase, no dashes or braces if you need them, then Copy all or download a .txt file.
UUID v4 vs. v7: which should you use?
Version 4 is 122 random bits. It reveals nothing about when or where it was made, which makes it ideal for public identifiers and anything security-adjacent. Version 7, standardized in RFC 9562 (2024), starts with a 48-bit Unix timestamp in milliseconds followed by random bits, so v7 IDs sort by creation time.
That ordering matters for databases. Random v4 primary keys land all over a B-tree index, causing page splits and poor cache locality as tables grow; v7 keys append near the end of the index like an auto-increment integer, while still being unique across servers. The trade-off: anyone can read the creation time from a v7 ID.
| UUID v4 | UUID v7 | |
|---|---|---|
| Sortable by creation time | No | Yes (millisecond precision) |
| Random bits | 122 | 62–74 per millisecond |
| Reveals creation time | No | Yes |
| Best for | Public IDs, tokens, file names | Database primary keys, event and log IDs |
Can two UUIDs collide?
In practice, no. With 122 random bits you would need to generate about 2.7 quintillion (2.7 × 1018) v4 UUIDs to have a 50% chance of a single duplicate. That holds only with a cryptographically secure random source like the one used here — generators built on Math.random() can and do collide.
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Frequently asked questions
Is my data sent to a server?
No. This tool runs entirely in your browser with JavaScript, so your data never leaves your device and isn't logged or stored. You can even use it offline once the page has loaded.
What's the difference between a UUID and a GUID?
Nothing technical — GUID is Microsoft's name for the same 128-bit identifier. Windows tools often show GUIDs in uppercase with braces, which you can enable above.
Can I get the timestamp back out of a v7 UUID?
Yes. Open “Inspect a UUID” under the generator and paste it — the first 48 bits are decoded into a date. It also reads the time from v1 and v6 UUIDs.
Are the v7 UUIDs in a batch in order?
Yes. UUIDs generated within the same millisecond use a 12-bit counter (RFC 9562 method 1), so every batch sorts in exactly the order it was generated.
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