Seeded Random Number Generator
Generate repeatable random numbers from a text seed. The same seed always returns the same list, with ranges, decimals, a no-duplicates mode and CSV export.
10 numbers from seed “bytetools”
Your seed is hashed with xmur3 into a 32-bit state and fed to the mulberry32 PRNG, so the sequence is reproducible on any device and in any browser. That makes it ideal for test fixtures and simulations — but it is deliberately predictable, so never use it for passwords, tokens or anything security-related.
What is the Seeded Random Number Generator?
A seeded random number generator produces a list that looks random but can be reproduced exactly. Type a seed such as your project name, set the range and how many numbers you want, and you get a list.
- Reproducible output from any text seed
- Whole numbers or decimals with up to 8 decimal places
- Optional draw without replacement for unique values
- Mean, median, lowest and highest shown for every run
- One-click copy plus CSV and JSON download
- Runs entirely offline in your browser
How to use the Seeded Random Number Generator
- 1
Type a seed, or press New seed to get a random one.
- 2
Set how many numbers you want, plus the minimum and maximum of the range.
- 3
Choose whole numbers or decimals, and set the decimal places if you picked decimals.
- 4
Tick No duplicates if every number in the list must be different.
- 5
Copy the list, or download it as CSV or JSON to use as a fixture.
About the Seeded Random Number Generator
A seeded random number generator produces a list that looks random but can be reproduced exactly. Type a seed such as your project name, set the range and how many numbers you want, and you get a list. Come back tomorrow, type the same seed, and you get the identical list — which is what makes it so useful for test fixtures and simulations.
Your seed is hashed with the xmur3 function into a 32-bit state, and that state drives the mulberry32 generator. Both are small, well-tested algorithms that behave identically in every browser, so a seed you share with a colleague produces the same numbers on their machine as on yours. You can draw whole numbers or decimals, and optionally forbid duplicates.
Everything runs in your browser. The seed and the numbers never leave your device, nothing is uploaded, and the tool keeps working offline. Because the sequence is deliberately reproducible it is also predictable, so use it for test data and never for passwords, tokens or anything that needs to be secret.
Frequently asked questions
What does seeding a random number generator actually do?
Seeding sets the generator's starting state. Because the algorithm is deterministic, the same starting state always produces the same sequence of numbers. Changing a single character in the seed produces a completely different list.
Will the same seed give the same numbers on a different computer?
Yes. The xmur3 and mulberry32 algorithms use only 32-bit integer maths, which behaves identically in every JavaScript engine. A seed that produces a given list here will produce that same list in any browser on any operating system.
Is a seeded random number generator safe for passwords?
No, and you should never use one for that. Anyone who knows or guesses your seed can reproduce every number you generated. For passwords and tokens use a generator based on crypto.getRandomValues instead.
How do I generate random numbers without duplicates?
Tick the No duplicates box. The tool then draws without replacement and rejects any repeat. If you ask for more unique numbers than the range can hold — say 50 unique values between 1 and 10 — it tells you rather than looping forever.
Is mulberry32 a good random number generator?
For simulations, shuffling test data and procedural generation, yes. It passes standard statistical randomness tests and is very fast. It is not cryptographically secure, so it should never protect anything sensitive.
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