Zerdly

Random Number Generator

Generates random integers or decimals within a range, optionally unique.

100% FreeRuns in your browserBasic
How to use this calculator

Input

Tool
Randomness

Up to 100,000. Ranges beyond ±2^53 use exact large-range (BigInt) mode.

Output

Press Generate.

Runs entirely in your browser. Your input is not uploaded or stored.

How the method works

Six draws from 1–6 without replacement
Illustrative method
Six draws from 1–6 without replacementSix tiles numbered 1 to 6 form the range. Drawing six values without replacement removes each value once picked, so the result is an ordering of all six — here 4, 1, 6, 2, 5, 3 — with chances 1 in 6, 1 in 5, down to 1 in 1.Range 1–6, both ends included123456draw 6, no repeats4#11/61#21/56#31/42#41/35#51/23#61/1Each value once → a permutation (count 7 rejects)
Range 1–6 inclusive (6 values). Without replacement each draw picks uniformly from the values still left (1/6, 1/5, 1/4, 1/3, 1/2, 1/1), so six draws give a permutation such as 4, 1, 6, 2, 5, 3. Asking for 7 values without replacement is rejected; with replacement repeats are allowed.

Secure mode maps random bits to a range by rejection sampling, so no value is favoured; seeded mode is reproducible but not secure. Fixed example values for illustration — not your result.

How to use this calculator

  1. Set min, max and step (1 for whole numbers, 0.1 for tenths), how many, and whether repeats are allowed — or switch to shuffling a list. Whole numbers beyond ±2^53 (up to 40 digits, at most 2^128 possible values) use an exact large-range mode.
  2. Keep Secure randomness, or choose Seeded to get the same sequence again from the same seed.
  3. Press Generate, then copy the lines or download CSV or JSON. More than 1,000 values are drawn in the background, with Cancel.

How it works

Secure mode uses the browser's crypto.getRandomValues and maps it to your range by rejection sampling, so every value is equally likely (the common x % n shortcut is biased). Large ranges use exact BigInt arithmetic and bitmask rejection: draw just enough random bits, retry if the value is outside the range.

Decimals are picked from the exact grid min, min + step, … max, so both endpoints are as likely as any other value. Without repeats the draw is a uniform sample; shuffles use Fisher–Yates.

Seeded mode (sfc32 seeded by cyrb128, version 1) is reproducible and NOT cryptographically secure.

Worked example

1 to 6, six values, no repeats. Always a permutation of 1–6. Asking for seven without repeats is refused, because only six values exist.

Common mistakes

  • Using seeded output for passwords or keys.
  • Rounding random decimals yourself — the endpoints then come up half as often.
  • Treating a histogram of a few dozen draws as proof of bias.

Tips

  • Runs entirely in your browser. Your input is not uploaded or stored.

Frequently asked questions

Is it cryptographically secure?

Secure mode draws from the browser's cryptographic source, but this page is for picks, sampling and testing — not for generating passwords, keys or audited prize draws.

Privacy?

Runs entirely in your browser. Your input is not uploaded or stored.

Related tools

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Cite this tool

Zerdly. (2026). Random Number Generator. Retrieved from https://www.zerdly.com/tools/random-number-generator/

Tip: Enter any known values to calculate the remaining results.

Designed to run locally in your browser. Tool inputs are not intentionally stored by Zerdly unless stated otherwise.