UUID v4 Generator

UUID Generator — Generate Version 4 Universally Unique IDs

A UUID (Universally Unique Identifier) is a 128-bit identifier formatted as a 36-character string like 550e8400-e29b-41d4-a716-446655440000. They're designed to be generated without any central coordination and are statistically guaranteed to be unique — you could generate trillions of UUIDs and the probability of a collision is negligible. This makes them ideal for distributed systems where you need unique IDs across multiple services or databases.

What is UUID Version 4?

UUID v4 is the most common type — it's randomly generated. 122 of the 128 bits are random (the remaining 6 bits identify the version and variant). The randomness comes from a cryptographically secure random number generator, making collisions essentially impossible in practice. Other UUID versions (v1, v3, v5) are derived from timestamps, MAC addresses, or namespace + name hashing — v4 is the simplest and most widely used when you just need a unique ID.

Common use cases

Database primary keys: Instead of auto-incrementing integers, many modern databases use UUIDs as primary keys. This allows rows to be created across multiple servers or clients without coordination — each client generates its own UUID and there's no risk of ID collision. This is especially useful for distributed databases and systems that need to work offline and sync later.

API resource identifiers: Exposing database auto-increment IDs in your API URLs (/users/42) is a security smell — users can guess other users' IDs by incrementing the number. UUIDs like /users/550e8400-e29b-41d4-a716-446655440000 are not guessable.

File naming for uploads: When users upload files to a server, saving them with their original filename creates risks (name collisions, path traversal attacks). Generating a UUID filename for each upload ensures uniqueness without depending on the user's filename.

Session tokens and transaction IDs: Generating a UUID for each session, transaction, or request gives you a unique reference that can be logged, traced, and referenced — without needing a central counter.

Frontend development and testing: When you need temporary unique keys for React list items, mock data for a UI, or placeholder IDs for a prototype, generate a batch of UUIDs here and paste them into your fixtures or test data.

Event sourcing and message queues: Events in event-sourced systems need unique IDs so they can be deduplicated and replicated safely. UUIDs are the standard choice.

How to use it

Click generate to create one or multiple UUIDs. Use the "Generate 10" option to create a batch at once. Copy individual UUIDs using the copy button on each row, or copy all of them at once. Download as a .txt file if you need a large batch.

UUID format

UUIDs are displayed in canonical form: eight hexadecimal characters, then three groups of four characters each, then twelve characters, all separated by hyphens — xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx. They're case-insensitive, but lowercase is the conventional form. Most database systems and APIs accept either case.

Tips

If you're using UUIDs as database primary keys, be aware that random UUID v4 keys cause index fragmentation in B-tree indexes in some databases (especially MySQL with InnoDB) because they're inserted in random order rather than sequentially. If this is a concern at scale, look into UUID v7 (time-ordered UUIDs) or database-specific solutions like PostgreSQL's built-in UUID type with the gen_random_uuid() function, which is also v4 but you're already on the database's native implementation.

Strip the hyphens from UUIDs if your database or system requires a compact 32-character hex string instead of the standard 36-character dashed format.

Limitations

This generator produces UUID version 4 only. Other versions (v1 — time-based, v3 — MD5 namespace hash, v5 — SHA-1 namespace hash) require different inputs and serve different use cases. If you specifically need v1, v3, or v5, use a library in your code rather than this browser tool.

The generated UUIDs are not stored anywhere — once you close the tab, they're gone. If you need to regenerate the same UUID later, that's not possible (that's the point of UUID v4 — they're unique and random every time). Save or use them before closing the tab.