What is the difference between UUID v4 and v7?

UUID v4 is fully random and unsortable. UUID v7 embeds a millisecond timestamp prefix, making it lexicographically sortable — much better for database index performance.

UUID vs ULID — which should I use?

ULID uses timestamp(48-bit)+random(80-bit) and is sortable, encoded in 26-char Base32 — shorter and URL-safe. UUID v4 has wider library support as the universal standard.

Are there performance issues using UUID as a database primary key?

UUID v4's randomness causes frequent B-Tree page splits, hurting write performance. Solutions: UUID v7 (time-sorted), ULID, or storing as binary with MySQL's UUID_TO_BIN().

What is the collision probability of UUID v4?

UUID v4 has 122 bits of randomness. Even generating a billion UUIDs, the collision probability is around 10⁻¹⁸ — practically negligible.

IDUUID Generator

Generate random UUID v4 strings

UppercaseNo dashes

1.cd179610-3798-4446-a92f-1ea3dafd4b33

Complete UUID Guide

UUID (Universally Unique Identifier) is a 128-bit identifier standardized in RFC 4122, represented as 32 hex digits with hyphens: 550e8400-e29b-41d4-a716-446655440000. It generates globally unique IDs without a central server, making it indispensable for distributed systems, microservices, and database primary keys.

UUID Versions: v1 / v4 / v7

UUID v1: MAC address + timestamp. Time-sortable but exposes the MAC address, raising privacy concerns.
UUID v4: Fully random. The most widely used version; crypto.randomUUID() is the modern standard. Collision probability is astronomically low.
UUID v7 (RFC 9562, 2024): Millisecond timestamp prefix makes it lexicographically sortable — dramatically better B-Tree index performance over v4.

UUID vs ULID vs Snowflake

Format	Length	Sortable	Notes
UUID v4	36 chars	No	Universal standard, widest library support
UUID v7	36 chars	Yes	DB index optimized, RFC 9562
ULID	26 chars	Yes	Base32, URL-safe, compact
Snowflake	64-bit int	Yes	Used by Twitter/Discord, requires central node

Database UUID Primary Key Trade-offs

Pros: No cross-server collisions, client-side pre-generation, security (prevents sequential ID exposure)
Cons (v4): Random insertion causes B-Tree page splits → write performance degradation, larger storage
Solutions: Use UUID v7 or ULID; in MySQL store as binary with UUID_TO_BIN(uuid, 1)

Real-World Usage — Distributed Systems

REST API: Client pre-generates ID and sends a PUT request, ensuring idempotency
Offline-first apps: Create records locally without network, sync later
Event sourcing: Unique event identification and deduplication
File/asset management: Collision-free storage uploads

FAQ

Q. UUID v4 or v7 — which should I pick?

For new projects using UUIDs as DB primary keys, prefer v7. If library compatibility is the priority, v4 is the safe choice.

Q. Can I use UUID directly in URLs?

Yes — hyphens are URL-safe characters so no encoding is needed. For shorter URLs, consider the No dashes option or ULID.

Q. Are UUIDs generated here cryptographically safe?

Yes. This tool uses the browser's crypto.randomUUID(), a CSPRNG. All processing is local — nothing is sent to a server.

Q. How many can I generate at once?

Up to 50 at a time in this tool. For larger batches, call crypto.randomUUID() in a loop in Node.js — it is synchronous and extremely fast.

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