Tip: Press Ctrl+Enter to generate
Output
Generated UUIDs will appear here…
UUID Generator
A UUID (Universally Unique Identifier) is a 128-bit value used to uniquely identify information in computer systems. This tool generates all major UUID versions: v1 (time-based), v4 (random), v5 (name-based SHA-1), v6 (sortable time-based), and v7 (Unix timestamp, sortable). All generation happens entirely in your browser — nothing is sent to a server.
What this tool does
This generator supports all major UUID versions — v1, v4, v5, v6, and v7 — and runs entirely in your browser with no server calls. Select the version, set how many you need (up to 100), and click Generate. The Uppercase and No hyphens options apply to every version. v4, v6, and v7 use crypto.getRandomValues() for their random components; v5 uses the SubtleCrypto SHA-1 implementation built into your browser. Nothing is logged or stored.
How to use it
- Set the count field to how many UUIDs you need (up to 100 per batch).
- Click Generate or press Ctrl+Enter.
- Check Uppercase if your system requires capital hex letters (e.g. some SQL Server contexts).
- Check No hyphens if you're storing UUIDs as a 32-character hex string without separators (common in MySQL binary columns).
- Use Copy All to copy the full list — one UUID per line — for pasting into SQL, config files, or test fixtures.
When to use UUIDs (and when not to)
- Database primary keys: UUIDs let you generate IDs client-side without touching the database first, which is useful in distributed systems or offline-first applications. The trade-off: random v4 UUIDs fragment B-tree indexes badly at scale. If insert performance matters, consider UUID v7 (time-sorted) or ULIDs instead.
- File uploads: Rename uploaded files to a UUID before writing to disk. This prevents path traversal attacks from user-supplied filenames and ensures no collisions even across concurrent uploads.
- Tokens and identifiers: Password reset links, magic login tokens, invite codes — UUIDs work well here. They're unguessable and long enough to be brute-force resistant.
- When not to use them: Don't use UUIDs where you need sequential IDs for human reference (order numbers, ticket IDs). Auto-increment integers are simpler and more compact. Don't use them as URL slugs — they're ugly and meaningless to users.
Frequently Asked Questions
What is a UUID v4 generator?
A UUID v4 generator creates universally unique identifiers using cryptographically random numbers. Each v4 UUID is 128 bits, formatted as 8-4-4-4-12 hex characters. This tool generates them entirely in your browser using crypto.getRandomValues() — no server is involved.
How do I generate a UUID online for free?
Select your UUID version (v4 for random, v7 for time-sortable), set the quantity (1–100), and click Generate. Your UUIDs appear instantly. Use Copy All to copy the full list to your clipboard.
What is the difference between UUID v1 and UUID v4?
UUID v1 is time-based and includes your machine's timestamp and MAC address — it can reveal information about your system. UUID v4 is fully random and reveals nothing. For database IDs, tokens, and file names, UUID v4 is the safer and more private choice.
Is UUID v4 really unique? Can I get duplicates?
In practice, v4 collisions are effectively impossible. There are 2^122 possible v4 UUIDs. To have a 50% chance of a single collision, you'd need to generate 2.7 quadrillion UUIDs. Treat them as unique for any real-world application.
What is UUID v7 and when should I use it?
UUID v7 encodes a Unix timestamp in the most significant bits, making it time-sortable. Unlike v4, UUIDs generated in sequence are roughly ordered by creation time. This makes v7 far better for database primary keys — it avoids the index fragmentation that fully random v4 UUIDs cause at scale.
Want the full explanation? Read the guide: UUIDs vs Sequential IDs: A Practical Comparison → · UUID v4 Explained: How It Works and When to Use It →