UUID Generator: A Developer’s Guide to v1, v4, v7 and When to Use Each

TL;DR — The UUID Generator produces RFC 4122 v4 (purely random) and v7 (time-ordered) UUIDs in your browser. Use v4 for tokens, secrets, and ad-hoc IDs; use v7 for database primary keys where index locality matters. For hashing or random integer needs, see the Hash Generator and Random Number Generator.

Why auto-increment IDs are a liability

Integer primary keys (1, 2, 3, …) work on a single SQL server. In a modern distributed setup — read replicas, sharding, offline-first mobile apps, multi-region writes — they fall over for three reasons:

• Coordination cost. Two servers can’t both safely mint ID #1000 without round-tripping to a central authority.
• Enumeration leaks. A URL like /orders/4823 tells competitors your total order count. Incrementing by 1 makes scraping trivial.
• Client-side creation. Mobile and offline apps need to create records before they ever reach the server. Integers can’t do that without conflict.

What a UUID actually is

A UUID is a 128-bit identifier, usually printed as 32 hex characters with dashes: 550e8400-e29b-41d4-a716-446655440000. The version digit (the first character of the third group) tells you how it was generated.

Which UUID version do you need?

Version	How it’s built	Use it for
v1	Timestamp + MAC address	Avoid — leaks the host MAC. Legacy only.
v4	122 bits of random data	Tokens, secrets, session IDs, anywhere unpredictability matters
v7	48-bit Unix ms timestamp + 74 random bits	Database primary keys — sortable and index-friendly

The pragmatic rule: v4 for tokens, v7 for primary keys. v7 was added to RFC 9562 in 2024 specifically because v4’s pure randomness destroys B-tree index locality and tanks insert performance on large Postgres / MySQL tables. v7 keeps the uniqueness guarantees but sorts naturally by creation time.

Generating UUIDs in 5 seconds

1. Open the UUID Generator.
2. Pick the version (default v4) and a count (1–1000).
3. Click Generate. Copy a single UUID, or download the batch as JSON, CSV, or newline-delimited text.

Code samples

// JavaScript / Node 19+
crypto.randomUUID();
// → '550e8400-e29b-41d4-a716-446655440000'

// Python 3
import uuid
uuid.uuid4()

// PostgreSQL 13+
SELECT gen_random_uuid();

// PostgreSQL 18+ (v7)
SELECT uuidv7();

Common mistakes to avoid

• Using Math.random(). It’s not cryptographically secure and collisions become real at scale. Always use the platform’s crypto.randomUUID().
• Storing UUIDs as VARCHAR(36). Use a native UUID column type — half the storage and faster comparisons.
• Picking v4 for primary keys on a 100M-row table. Random inserts wreck cache locality. Move to v7.
• Treating UUIDs as secrets. v4 has 122 bits of entropy and is unguessable, but if you put it in a URL, treat it as semi-public — anyone the link is shared with can use it.

Privacy

The UUID Generator uses your browser’s built-in crypto.getRandomValues() API — the same CSPRNG that backs TLS in Chrome and Firefox. No network call, nothing logged, works offline.

FAQ

Are UUIDs really unique?

With v4, the chance of collision among 1 billion generated UUIDs is roughly 1 in 10¹⁸. For all practical purposes, yes.

What’s the difference between UUID and GUID?

None functionally — GUID is Microsoft’s name for the same 128-bit identifier. The generator output works in both ecosystems.

Should I use ULID or UUID v7?

UUID v7 is now standardized in RFC 9562 and supported natively in major databases. ULID gave us most of v7’s benefits earlier, but v7 is the modern answer.

Can I generate UUIDs offline?

Yes — load the page once, then disconnect. Generation uses local randomness only.

Tools to bookmark

• UUID Generator — v4 + v7, bulk export.
• Hash Generator — MD5, SHA-1/256/512 for any text or file.
• Random Number Generator — cryptographically secure integers in any range.
• All coding tools →