UUID v4 (GUID) Generator

UUID/GUID Generator: what it does and how to use it

This page generates UUID version 4 identifiers (also commonly called GUIDs in Microsoft documentation). A UUID is a 128-bit value typically formatted as 32 hexadecimal characters displayed in five groups separated by hyphens, for example:

123e4567-e89b-12d3-a456-426614174000

Privacy note: this tool runs in your browser. Generated IDs are not sent to a server by the generator logic.

How to use this generator

1. Enter how many UUIDs you want (between 1 and 10).
2. Select Generate to create the IDs.
3. Select Copy to copy all generated UUIDs (one per line).

What is a UUID (and how is it structured)?

A UUID is a standardized identifier defined by RFC 4122. Most tooling expects the canonical “8-4-4-4-12” hex format:

xxxxxxxx-xxxx-Mxxx-Nxxx-xxxxxxxxxxxx

• M is the version (for v4 this is always 4).
• N encodes the variant (for RFC 4122 UUIDs, the high bits correspond to values 8, 9, a, or b in that position).

UUID v4 randomness and the size of the ID space

UUID v4 uses random bits for most of its content. After accounting for version and variant bits, there are 122 random bits available, so the total number of possible v4 UUIDs is:

This space is enormous, so accidental collisions are extremely unlikely in typical applications. Still, UUIDs are best described as probabilistically unique, not mathematically guaranteed unique.

When developers use UUIDs (and when they don’t)

UUIDs are popular because they can be generated without coordination (no central counter required) and are hard to guess compared to sequential IDs. Common uses include:

• Database keys in distributed systems (reduces ID coordination).
• Client-generated IDs for offline-first apps (generate before syncing).
• Trace/event IDs in logging and observability pipelines.
• File/object names where predictability is undesirable.

However, UUIDs are not always the best choice. They can be larger than integer IDs, less index-friendly in some databases, and they do not automatically provide ordering (v4 is effectively random). If you need time ordering, consider ULIDs or UUID v7 (where supported).

Worked example

Suppose you are creating client-side “draft” records before saving to a server.

1. Set Number of UUIDs to 3.
2. Select Generate.
3. You might receive output similar to:

f47ac10b-58cc-4372-a567-0e02b2c3d479
9f1c2a0d-0f7c-4a58-9c19-3e6d20a6d8be
6ba7b810-9dad-41d1-80b4-00c04fd430c8

You can now attach one UUID to each draft item, then send them to your API; the server can store them as-is (or map them to internal IDs).

UUID versions at a glance

Interpreting and validating the output

This generator outputs one UUID per line in lowercase hexadecimal with hyphens. Many systems accept uppercase as well, but some validators are strict about format. A basic (format-only) pattern for an RFC 4122 v4 UUID is:

^[0-9a-f]{8}-[0-9a-f]{4}-4[0-9a-f]{3}-[89ab][0-9a-f]{3}-[0-9a-f]{12}$

Note: regex checks format, not true randomness.

Limitations & assumptions

• UUID version: This tool generates version 4 (random) UUIDs only.
• Randomness source: It prefers crypto.randomUUID() when available. If unavailable, it falls back to a non-cryptographic method; results may be less suitable for security-sensitive uses.
• Not a security guarantee: UUIDs are not authentication tokens. Don’t use them as the only secret protecting access to sensitive data.
• Probabilistic uniqueness: Collisions are extremely unlikely but not impossible. Critical systems should still enforce uniqueness where required (e.g., database unique constraint).
• Output limits: You can generate between 1 and 10 UUIDs per click to keep the UI fast and readable.
• Formatting: Output is lowercase with hyphens; some systems may require braces or different formatting (you may need to transform it).

FAQ

Is a GUID different from a UUID?

In practice, “GUID” is Microsoft’s name for a UUID. Most GUIDs you see today follow the same 128-bit UUID format.

Are UUID v4 values truly random?

When generated via crypto.randomUUID(), they use the browser’s cryptographically strong random source. If a fallback is used, randomness quality may be lower.

Can I use UUIDs as secrets (like API keys)?

No. UUIDs are identifiers, not access secrets. Use dedicated token/key generation for secrets.

Why limit generation to 10 at a time?

It keeps the interface simple and avoids accidental huge output. If you need more, generate multiple batches.