UUID Generator

About the UUID Generator

This online UUID generator creates RFC 4122 version 4 identifiers using your browser's native crypto.randomUUID call, so every ID comes from the same cryptographically secure random source used elsewhere in the browser rather than a weaker pseudo-random generator. You can produce a single UUID or a batch of up to 100 at once.

A version 4 UUID is a 128-bit value where 122 bits are random and the rest are fixed version and variant markers. That gives roughly 5.3 x 10^36 possible values, so two independently generated v4 UUIDs colliding by chance is not a realistic concern at any volume a normal application will ever produce.

Reach for it whenever you need an identifier that does not require a central authority to hand it out: primary keys for a new database table, request or trace IDs to correlate logs across services, idempotency keys for an API call, keys for test fixtures, or unique filenames for uploads.

Set the count field to anything from 1 to 100, click generate, and the tool produces that many UUIDs at once. Changing the count field alone does not regenerate the list; you need to press generate again to get a fresh batch at the new size.

Generation happens entirely in your browser using crypto.randomUUID. No request is sent anywhere to obtain or register the identifiers, so nothing about what you generate, or how many, is visible to a server.

How to use it

1. Enter how many UUIDs you want in the count field, from 1 to 100.
2. Click generate to create that many version 4 UUIDs at once.
3. Review the list, one UUID per line.
4. Click copy all to place every UUID on your clipboard, newline-separated.
5. Change the count and click generate again for a different batch size; the count field alone does not regenerate the list.
6. Select and copy a single line manually if you only need one UUID out of a larger batch.

Examples

• Generate a single UUID for a new database row: 4f9ac409-1f7e-4efa-875b-793972434277.
• Generate 100 at once to seed test fixtures, then copy all and paste straight into a SQL seed script or JSON mock file.
• Use one as a request correlation ID in application logs, for example 62dcac80-6596-4059-862a-09c6d7df97f6, so a single request can be traced across microservices.
• Use one as an idempotency key so calling a payment API twice with the same intent does not create two charges.
• Notice the third block always starts with 4 (4efa, 4775, 4059) and the fourth block always starts with 8, 9, a or b (875b, a27d, 862a): those are the fixed version and variant markers that make it a v4 UUID.

Anatomy of a version 4 UUID

A UUID is 36 characters long: 32 hex digits split into five groups of 8-4-4-4-12, separated by hyphens (xxxxxxxx-xxxx-4xxx-yxxx-xxxxxxxxxxxx). The first character of the third group is fixed to 4 and marks the version. The first character of the fourth group is fixed to one of 8, 9, a or b and marks the RFC 4122 variant. Every other hex digit is drawn from the browser's secure random source, giving 122 bits of randomness in total.

• Format: 8-4-4-4-12 hex digits, 36 characters including 4 hyphens.
• Version nibble: always 4, first character of the third group.
• Variant nibble: always 8, 9, a or b, first character of the fourth group.
• Random bits: 122 of 128 total, about 5.3 x 10^36 possible values.

UUID versions compared

• v1: time-based plus MAC address, sortable but can leak the generating machine's identity.
• v4: fully random, this tool's output, no ordering, no metadata leakage.
• v7: time-ordered with an embedded millisecond timestamp, sortable and increasingly used for database primary keys.
• Short non-UUID IDs (see the ids generator): a smaller footprint than a full UUID, but not RFC 4122 compliant, so not a drop-in replacement everywhere a UUID is expected.

Common UUID mistakes

• Using v4 UUIDs as the primary key on a large, high-write table and being surprised by poor index locality; random values scatter inserts across a B-tree, unlike sequential or v7 IDs.
• Assuming a hyphen-stripped or upper-cased UUID is a different identifier. Case and hyphens are just formatting; the underlying 128-bit value is identical.
• Changing the count field and expecting the list to refresh automatically. The new count only takes effect on the next click of generate.
• Trusting a v1 UUID for anonymity. It embeds a timestamp and often a MAC-derived node ID, unlike the fully random v4 UUIDs this tool produces.

Frequently asked questions