Toolivaro

Free UUID Generator

Generate RFC 4122 version-4 UUIDs from cryptographically secure randomness — one at a time or in bulk, fully local.

Processed locally in your browser

1–100 per batch.

Format

How is the result calculated?

Three test fixtures

Generate three UUIDs for seed data. Each value has the version-4 nibble (a 4 in the third group) and the variant bits (8, 9, a, or b starting the fourth group), e.g. 7f3a9c21-4d2e-4b8a-9c1e-2f3a4b5c6d7e — the pattern is visible at a glance so a hand-typed fake is easy to spot.

Input Value
count 3
format lowercase, hyphenated
Result 3 valid RFC 4122 v4 UUIDs, each verified against version and variant bits

What is the formula and its assumptions?

Version 4 construction

uuid = 122 random bits, with version = 0100 and variant = 10 fixed

Symbol Meaning
version the high nibble of the third group set to 4
variant the two high bits of the fourth group set to 10

Randomness comes from the platform’s cryptographically secure getRandomValues.

What are the most common mistakes?

  • Using Math.random() for identifiers — it is not cryptographically secure; this tool uses getRandomValues.
  • Accepting any 8-4-4-4-12 string as a v4 UUID — the version and variant bits must also match.
  • Hand-typing UUIDs for fixtures — one wrong character and the value is invalid.
  • Generating identifiers on a server that logs them — this tool is fully local.

What are the assumptions and limitations?

  • Version 4 only: the tool generates and validates v4; v1, v3, v5, and time-ordered v7 are not supported.
  • Bulk generation is capped at 100 values per batch to keep the page responsive.
  • Uniqueness is probabilistic, not guaranteed — the tool states the odds rather than promising absolute uniqueness.

Where do the numbers come from?

Last reviewed August 5, 2026 · Version 1.0.0 · Toolivaro does not guarantee external content.

Frequently asked questions

Why does my generated UUID always have a 4 in the third group?

That is the version field: RFC 4122 version 4 fixes the high nibble of that byte to 0100 (hex 4). Every valid v4 UUID shows this — it is not a bug, it is the format.

Are two generated UUIDs guaranteed to differ?

No generator can guarantee uniqueness — v4 provides 122 random bits, so collisions are astronomically unlikely (about 1 in 2^61 for two billion values) but not impossible. The tool uses the platform’s cryptographic randomness, which is the strongest source available in the browser.

What does the validator check?

The shape (8-4-4-4-12 hex groups), the version-4 nibble, and the RFC variant bits. A string with the right dash pattern but the wrong version — like a v1 or v3 UUID — is correctly rejected.

Found a mistake or have a correction? Report it — we review every correction.