What is a UUID?
A UUID (Universally Unique Identifier), also called a GUID (Globally Unique Identifier), is a 128-bit identifier formatted as 32 hexadecimal characters separated by hyphens: xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx. UUIDs are designed to be unique across time and space without requiring a central authority to assign them — making them ideal for distributed systems.
UUIDs are defined by RFC 4122 and come in several versions. This tool supports v4 (random) and v1 (time-based).
UUID v4 vs UUID v1
- UUID v4 (Random) — Generated using cryptographically random numbers. 122 of the 128 bits are random, making collisions astronomically unlikely. This is the most widely used version and the recommended choice for most use cases.
- UUID v1 (Time-based) — Incorporates the current timestamp and a node identifier (MAC address in the spec). Because they embed time, v1 UUIDs are sortable and can reveal when they were created. In this browser-based tool, the node is randomized since MAC addresses are not accessible from JavaScript.
How to Use This Tool
- Select V4 or V1 using the version toggle.
- Click any UUID in the list to instantly copy it to your clipboard.
- Use Add one to append a new UUID to the list.
- Enter a number (1–100) and click Generate bulk to produce multiple UUIDs at once.
- Click Copy all to copy the entire list as newline-separated text.
- Click Regenerate all to replace all current UUIDs with fresh ones.
Common Use Cases
- Database primary keys — UUIDs make excellent primary keys in distributed databases where auto-incrementing integers would conflict across multiple nodes.
- Session and token IDs — Random v4 UUIDs are suitable as session tokens, API keys, or one-time tokens due to their unpredictability.
- File and asset naming — Naming uploaded files with UUIDs prevents collisions and avoids exposing sequential IDs.
- Message and event IDs — In event-driven systems and message queues, UUIDs uniquely identify each event or message.
Frequently Asked Questions
Can two UUIDs ever be the same?
Theoretically yes, but practically never. A v4 UUID has 122 random bits, giving 2¹²² possible values — roughly 5.3 × 10³⁶. The probability of generating a duplicate even after generating billions of UUIDs is effectively zero.
Are UUIDs safe to use as passwords or secrets?
No. While v4 UUIDs are random, they have a fixed format and length (32 hex chars = 128 bits, with 6 bits fixed). They are not designed for use as passwords or cryptographic secrets. Use a dedicated password generator or a cryptographically secure key generator instead.
Does it send UUIDs to a server?
No. All UUIDs are generated locally in your browser using the crypto.randomUUID() API (for v4) which uses the operating system's cryptographically secure random number generator. Nothing is sent anywhere.