UUID Generator: Create RFC 4122 Compliant UUIDs (v4) Online

What Is a UUID and Why Is It Used?

A UUID is a 128-bit identifier standardized by RFC 4122. Its 36-character canonical text form consists of 32 hexadecimal digits and four hyphens arranged as 8-4-4-4-12 characters. UUIDs are used when a system needs to generate unique identifiers without a central authority — unlike auto-incrementing integers, UUIDs can be generated on any client or server without coordination and are still practically guaranteed not to collide.

There are several UUID versions: v1 uses the current timestamp and MAC address (leaks information), v3 and v5 are deterministic hashes of namespace and name, and v4 uses random data. UUIDv4 is preferred for most use cases because it reveals no information about when or where it was generated and has the strongest unpredictability properties.

The probability of two UUIDv4 values colliding is astronomically small. Generating 1 billion UUIDs per second for 85 years would be needed to reach a 50% probability of a single collision. For practical purposes, UUIDv4 collision can be treated as impossible.

How to Use This Tool

Generating UUIDs is simple and fast.

1. 1

   Set the quantity

   Use the quantity field to specify how many UUIDs to generate at once. You can generate 1 to 1000 UUIDs in a single click, useful for seeding test databases or pre-generating identifiers.

2. 2

   Choose formatting options

   Select whether you want the output in standard lowercase (the most common format), uppercase, or with the hyphens removed (for systems that store UUIDs as compact 32-character hex strings).

3. 3

   Click Generate

   Press Generate to produce the specified number of UUIDs. Each UUID is independently generated from fresh cryptographic random data — there is no sequential or predictable relationship between them.

4. 4

   Copy individual or all UUIDs

   Click the Copy button next to any individual UUID to copy just that one, or click Copy All to copy the entire list as a newline-separated string suitable for pasting into a file or script.

5. 5

   Use in your application

   Paste the UUID(s) directly into your database, code, or configuration. For database use, store UUIDs as the native UUID type if your database supports it, or as a CHAR(36) or BINARY(16) column for efficiency.

Common Use Cases

UUIDs are used throughout software development and system design.

• Database primary keys for distributed systems where multiple servers must generate IDs without coordination and without risk of collision.
• API resource identifiers in RESTful APIs where exposing sequential integer IDs would reveal business information (e.g., how many users or orders exist).
• Session identifiers, correlation IDs, and request trace IDs in web applications and microservices for tracking requests across systems.
• File and object names in cloud storage (S3, GCS) where unique, non-guessable names prevent unauthorized access to unprotected objects.
• Generating test data fixtures, mock IDs, and placeholder values when developing or testing applications that require UUID-formatted inputs.

Tips and Best Practices

Use UUIDs effectively in your systems with these recommendations.

• Use the native UUID type in your database rather than storing UUIDs as VARCHAR strings — databases like PostgreSQL have a native UUID type that stores values as 16 bytes instead of 36, saving storage and improving index performance.
• For high-throughput systems where UUID v4 index fragmentation is a concern (due to randomness causing scattered B-tree insertions), consider UUID v7, which is time-ordered and has much better insert performance.
• Never generate UUIDs client-side for security-sensitive identifiers like session tokens — generate them on the server and return them to the client. Client-side generation is fine for non-security identifiers.
• When using UUIDs as file names or URL components, use the compact form (no hyphens) or Base64url-encode the 16 binary bytes to save characters.
• Do not assume a UUID is secret just because it is unguessable. If a resource is sensitive, implement proper access control — do not rely solely on the ID being hard to guess.

Frequently Asked Questions