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uuid-generator

A UUID (Universally Unique Identifier) is a 128-bit value designed to be globally unique without coordination — anyone, anywhere can generate one and the chance of collision is effectively zero. The ZTools UUID Generator produces RFC 9562-compliant UUIDs in versions 1 (timestamp + MAC), 4 (random — most common), and 7 (timestamp-prefixed sortable, the modern preferred version), with bulk generation up to 10,000 at once for database seeding. Version 4 uses crypto.getRandomValues(), the same CSPRNG that the password generator uses, so the UUIDs are not just unique but unpredictable.

Use cases​

Generating primary keys for new database rows​

Use UUID v7 if your database supports it — the timestamp prefix means rows are inserted in approximate insertion order, preserving B-tree locality and cutting index bloat. For older databases, v4 is fine; just accept random insert order.

Idempotency keys for HTTP requests​

Stripe, Square, and most payment APIs accept an Idempotency-Key header so retried requests don't double-charge. Generate a UUID v4 client-side, attach it to the request, and reuse it on retries within a 24-hour window.

Correlation IDs for distributed tracing​

Mint a UUID at the API gateway, propagate via X-Request-Id header to every microservice. When debugging, grep all logs for that ID to reconstruct the entire request flow. Pairs perfectly with structured logging.

Anonymous user IDs for analytics​

Generate a UUID v4 once, store in localStorage, and use as the user identifier for product analytics. No PII, no email; just a stable random ID that lets you measure retention without cookies.

How it works​

  1. Choose version — v4 (random — most common, default). v7 (timestamp-prefixed, sortable). v1 (legacy, MAC-based). NIL (the all-zero UUID, used as a sentinel).
  2. Set quantity — 1 (default) up to 10,000. Each is generated independently — collisions are mathematically impossible at this scale (you would need ~2^61 v4 UUIDs to have a 50% chance of any collision).
  3. Pick format — Hyphenated (xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx) is standard. No-hyphens, uppercase, braces (\{...\}), and Base64 are also offered for systems with non-standard expectations.
  4. Click Generate — For v4, the tool calls crypto.randomUUID() (browsers since 2022) or falls back to crypto.getRandomValues() + bit-twiddling for the version/variant fields. For v7, timestamp + random bytes per the RFC 9562 layout.
  5. Copy or download — Single UUID copies on click. Bulk generates as one-per-line text, optionally with comma or JSON-array separators. Download as .txt or .json for batch use.

Examples​

Input: Version: v4, quantity: 1

Output: a8f5f167-7a8c-4b9e-8f1a-3e7d2c9b4f8a

Input: Version: v7, quantity: 3

Output: 018d4a3a-5f00-7b6f-9c4d-... 018d4a3a-5f01-7c2d-8a3e-... 018d4a3a-5f02-7e1a-bf67-...

Frequently asked questions​

Which UUID version should I use?

For most cases, v7 if your stack supports it (better DB index locality, naturally sortable), otherwise v4. Avoid v1 (leaks the MAC address of the generator) and v3/v5 (name-based, only useful when you need deterministic UUIDs from a namespace).

Can two UUIDs ever be the same?

In theory yes, in practice no. The probability of collision among 1 billion v4 UUIDs is roughly 1 in 10^18. You're more likely to win the lottery 10 times than to generate a duplicate.

Is a UUID a secret?

It depends on context. v4 UUIDs are 122 bits of randomness, which is unguessable enough to use as a session token IF the rest of your security model assumes that. But v1, v3, v5, and v7 are partially predictable, so don't treat them as secrets.

Why is v7 better for database keys than v4?

v7 is timestamp-prefixed, so rows insert in roughly chronological order. This matches B-tree page layout, dramatically reducing index fragmentation in PostgreSQL/MySQL. v4 inserts at random positions, causing constant page splits.

How do I generate UUIDs in bulk?

Set the quantity slider up to 10,000. The tool generates each independently (no shared state) and outputs as newline-separated text or a JSON array. For more than 10,000, use a CLI tool — paste the output is the bottleneck, not generation.

Can I generate UUIDs offline?

Yes. Once the page loads, generation runs entirely in your browser. Disconnect from the network and generate as many as you want. Useful for isolated development environments.

Tips​

  • Default to v7 unless you have a specific reason to use v4. Better DB performance, no downside.
  • For session tokens, prefer a longer crypto-random token (32+ bytes) over a UUID — UUIDs have only 122 bits of entropy due to fixed version/variant bits.
  • When seeding test data, generate UUIDs once and check them into the test fixtures. Random-per-run UUIDs make tests non-reproducible.
  • Format your UUIDs consistently across the codebase (always lowercase, always hyphenated). Mixed formats break case-sensitive comparisons.

Try it now​

The full uuid-generator runs in your browser at https://ztools.zaions.com/uuid-generator — no signup, no upload, no data leaves your device.

Open the tool ↗

Last updated: 2026-05-05 · Author: Ahsan Mahmood · Edit this page on GitHub