Random Number Generator
Whole Numbers, Decimals And Primes

What A Random Number Generator Does For You

Sometimes you need a number that nobody chose. Maybe it is for a draw, a test, a game or a sample. However, your own head is a poor source, because people pick the same few numbers again and again.

A random number generator fixes that. First, set a smallest and a largest value. Then pick how many numbers you want. Press Generate, and the list appears.

Also, it makes more than whole numbers. It makes decimals, primes, bytes, binary strings, hex strings and codes of letters and digits. So one tool covers most random jobs.

Everything runs in your browser. So nothing leaves your device, and no server sees your numbers.

How The Random Number Generator Works

The tool asks your browser for random bytes. Then the browser draws them from the operating system, which gathers noise from the hardware. So the source is strong, and it suits draws and tests.

Then the tool maps those bytes onto your range. It throws away any value that would favour a low number. So every number in the range has exactly the same chance.

For more detail, see: MDN guide to getRandomValues.

Random Whole Numbers

Pick a smallest and a largest value. Both can be negative, and both count. So 1 to 6 can give a 1 and a 6. So use it for dice, raffles, seat numbers and sample picks.

Also, tick All different to draw without repeats, as with lottery balls. Then the tool never gives the same number twice. If you ask for more numbers than the range holds, it tells you.

Show Numbers In Binary, Octal Or Hex

Whole numbers and bytes can show in four bases. Pick Binary for ones and zeros, Octal for base eight, and Hexadecimal for base sixteen. Hex letters appear in capitals.

So you can build test data in the base you need. Then you copy it as it stands.

Random Decimal Numbers

Choose how many decimal places you want, from one to eight. The tool draws a number between your two values and rounds it. So both ends stay inside the range.

For example, 0 to 1 with four places gives values such as 0.4172. Then you can use them as chances, weights or test prices.

Random Prime Numbers

The tool lists every prime in your range with a sieve. Then it picks from that list. So each prime has the same chance. The largest value can reach ten million.

If no prime lies in your range, the tool says so. Also, tick All different to draw primes without repeats.

Random Bytes

A byte is a number from 0 to 255. Use it for test data, colour channels and small samples. Then show it in hex, and you get two characters for each byte.

Binary, Hex And Letter Strings

Pick the length and the count. Binary strings use 0 and 1. Hex strings use 0 to 9 and a to f. Letter and digit strings can use letters only, digits only, or both.

So use them for test ids, codes and sample data. For passwords, use the password generator instead, because it adds symbols and checks strength.

Sort And Format The List

First, keep the order, or sort from smallest to largest, or the reverse. Then pick a separator: a new line, a comma, a space or a tab. A comma list pastes well into code, and a tab list pastes well into a spreadsheet.

Is It Truly Random

A computer cannot flip a coin, so it uses hardware noise and maths. Your browser offers a cryptographic source, which is far better than the usual Math.random call. So the numbers suit draws and games.

However, for passwords and keys, use a tool made for that job. It adds the right length, the right symbols and a strength check.

Fair Draws And Giveaways

For a giveaway, number the entries from 1. Then set the range from 1 to the number of entries, and draw one value. Then take a screenshot of the result to show that the draw was fair.

Dice, Coins And Games

Set 1 to 6 for a die and 1 to 2 for a coin. Then draw as many times as you like. Also, for two dice, ask for two numbers, and add them up yourself.

Testing And Sample Data

Developers use random numbers to fill tables and to test edge cases. Set a large count, pick a comma as the separator, and paste the list into your code. Also, a byte list makes handy fake data.

Safe By Design

First, the tool works in your browser. It sends nothing, and it stores nothing. So your numbers stay yours.