Numarly

UUID / Random Number Generator

Generate UUIDs or random numbers, securely and instantly in your browser.

What is it?

This tool generates version-4 UUIDs (universally unique identifiers) or random numbers within a range, using cryptographically secure randomness directly in your browser.

Formula Explanation

A UUID v4 is a 128-bit value made almost entirely of random bits, with a few fixed bits marking its version and variant — the random portion is generated using crypto.randomUUID() (or crypto.getRandomValues() as a fallback), making collisions astronomically unlikely. Random numbers are drawn uniformly from your chosen range using the same secure random source, with an optional Fisher–Yates shuffle when duplicates are disallowed.

Example Calculation

A generated UUID looks like 3fa85f64-5717-4562-b3fc-2c963f66afa6 — 32 hexadecimal digits split into five groups.

How to Use

  1. Choose UUID v4 or Random Number mode using the tabs.
  2. For UUIDs, set how many to generate.
  3. For random numbers, set a min, max, count, and whether duplicates are allowed.
  4. Copy an individual value, or use Copy All to grab the full list.

Benefits

  • Uses cryptographically secure randomness (Web Crypto API), not a predictable pseudo-random source.
  • Generates multiple UUIDs or numbers at once, with a one-click copy for the full batch.
  • Supports unique (no-duplicate) random number sampling from a range, not just independent draws.

Use Cases

  • Generating unique identifiers for test data, database records, or API keys during development.
  • Picking a random winner or random sample from a numbered list without duplicates.
  • Creating placeholder IDs for mockups or prototypes.

What Your Result Means

With "No duplicates" checked, the tool can only generate up to as many numbers as exist in your chosen range — asking for more than that will show an error rather than silently repeating values.

Tips

  • UUID v4 values are not sequential or sortable by creation time — use a different ID scheme if ordering matters.
  • For a truly random sample without duplicates, always enable "No duplicates" rather than filtering repeats yourself.
  • UUIDs are safe to use as public identifiers since they don't encode any information about when or how they were created.

Common Mistakes

  • Assuming UUIDs are ordered by generation time — version 4 UUIDs are fully random, not time-based.
  • Requesting more unique numbers than the min-max range can supply.
  • Using Math.random()-based generators elsewhere for anything security-sensitive instead of a cryptographic source like this tool uses.

FAQs

Does this tool send generated values to a server?

No, UUIDs and random numbers are generated entirely in your browser using the Web Crypto API and are never transmitted anywhere.

How unique are the generated UUIDs?

Version 4 UUIDs have 122 random bits, giving roughly 5.3 x 10^36 possible values — collisions are practically impossible even generating billions of them.

Can I generate decimal (non-integer) random numbers?

This tool generates whole numbers within your range; for decimals, generate an integer over a scaled range and divide it by the appropriate power of ten.

Why did I get an error when generating unique numbers?

"No duplicates" mode can only return as many numbers as exist between your min and max — widen the range or reduce the count to fix it.

UUIDs and random numbers are generated locally in your browser and are never sent to or stored on a server.

Last updated: July 27, 2026