UUID v4 generator

Generate secure version 4 UUIDs with the Web Crypto API. Nothing leaves your browser.

UUID v4 contains 122 bits of randomness. Collisions are practically impossible.

Understanding UUID formats

Universally Unique Identifiers (UUIDs) are 128-bit values rendered as 32 hexadecimal characters separated into an 8-4-4-4-12 pattern. Different versions dictate how those bits are filled, which influences ordering, source data, and collision guarantees.

Version Source Sort order Typical usage Notes
UUID v1 Timestamp + MAC address Chronological Legacy systems needing time ordering Leakes host metadata. Avoid in privacy sensitive contexts.
UUID v4 122 bits of randomness Unordered Default choice for distributed IDs Collisions are astronomically unlikely when generated with CSPRNG.
UUID v7 Unix timestamp + randomness Roughly sortable Event stores, databases that benefit from time ordering Draft standard gaining adoption. Great compromise between randomness and sorting.

Choosing the right identifier

Pick the UUID version that suits your application's scaling, privacy, and ordering requirements. These scenarios outline when to stick with v4 and when to consider alternatives.

Stateless APIs

v4 is ideal when microservices or clients generate identifiers independently and you only care about uniqueness, not sort order.

Append-only databases

For workloads that benefit from chronological clustering, UUID v7 or ULIDs maintain time ordering while preserving compatibility with UUID tooling.

Security-sensitive tokens

UUIDs are predictable enough to enumerate once discovered. For secrets, issue cryptographically random bytes and deliver them over TLS, or use JWTs with proper claims.

Implementation guidelines

A few simple habits keep UUIDs reliable across environments and databases.

Check a UUID v4 in your application

Generate an identifier and check its shape, version and variant. Random identifiers should differ between runs.

JavaScript — modern browser

const id = crypto.randomUUID();
console.log(id);
console.log(id[14] === '4'); // version 4
console.log(/[89ab]/i.test(id[19])); // RFC variant

Python 3 — standard library

import uuid
value = uuid.uuid4()
print(value)
print(value.version)  # 4

UUID v4 has 122 random bits. Collision probability grows with the number generated; enforce database uniqueness and handle a conflict. A UUID is an identifier, not proof that the requester is authorized.

UUID Versions Explained

Universally Unique Identifiers (UUIDs) are 128-bit numbers used to identify information in computer systems. The standard defines several versions, each suitable for different use cases.

Popular Versions

  • UUID v1: Time-based + MAC address. Can compromise privacy (reveals the MAC address of the generator).
  • UUID v4: Randomly generated. The most common version for general use. Extremely low collision probability.
  • UUID v5: Name-based (SHA-1 hashing). Deterministic: same name + namespace = same UUID.
  • UUID v7: Time-ordered + random. Great for databases where sorting by creation time is important.

This tool generates UUID v4 using the browser's cryptographically secure random number generator (CSPRNG), ensuring high quality randomness.

UUID generator FAQ

What is a UUID and how is it structured?

A UUID is a 128-bit identifier rendered as 8-4-4-4-12 hexadecimal characters. Versions such as v4 or v7 control how the bits are derived—randomness for v4, timestamp plus randomness for v7.

How unlikely is a UUID v4 collision?

UUID v4 leaves 122 bits of randomness, making collisions astronomically unlikely. You can generate billions before a statistically significant collision chance appears.

When should I use UUID v4 versus UUID v7?

Choose v4 for maximum randomness and ease of generation. Select v7 when you need roughly sortable identifiers that still work with UUID-aware databases.

Are UUIDs secure enough for secrets?

UUIDs provide uniqueness, not confidentiality. They make great identifiers, but use randomly generated tokens or encrypted payloads for anything sensitive.

Does this generator send identifiers to a server?

No. HashyTools uses the Web Crypto API directly in your browser so generated UUIDs never leave your device.

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