Seed, in full
A generator's state has to begin somewhere, and the seed is that beginning. Two runs from the same seed produce identical output. Two runs from seeds differing by a single character produce sequences with no visible relationship, because the mixing step scatters small input differences across every output bit. Seeds are usually short, often a single 32-bit or 64-bit integer or a string hashed down to one, while the stream they produce is enormous.
The standards literature draws a distinction the word alone hides. NIST's recommendation for deterministic generators treats seeding as the point where genuine entropy enters, and requires the seed material for a security-relevant generator to come from an approved entropy source. A seed you chose yourself is a reproducibility device, not a security one, and the two uses pull in opposite directions.
Vibe Numbers builds its daily seed as a string. dailySeed in core/rng.ts joins, in order, the birth date if one is saved, the ISO calendar date, and the name of the tool, separating the parts with a middle dot. With no birth date the seed reads date·tool. With one it reads birthdate·date·tool. That string goes through xmur3 to become a 32-bit integer, and the integer initialises mulberry32. What follows from that construction is set out on the page explaining how the daily numbers are made.
- Probability
- Random seed, Seed value
A worked example
Two readers born on 1990-04-17 open the site on the same day. Both seeds start with 1990-04-17, carry the same ISO date and the same tool name, so xmur3 lands on the same 32-bit integer and mulberry32 runs the same stream. Their numbers match exactly. Change one character of the birth date and the hash lands somewhere unrelated, so the two sets share nothing beyond coincidence.
Sources
In the standards for deterministic random bit generators, seeding is the step at which entropy is introduced, and approved generators must be seeded from an approved entropy source.
NIST SP 800-90A Rev. 1, Recommendation for Random Number Generation Using Deterministic Random Bit Generators (June 2015)
See also
Where it comes up on this site
Seed: frequently asked
The calendar date is an ingredient of the seed rather than a clock ticking somewhere. Same string in, same numbers out, on every page load until the date rolls over.
Yes, by design. Same saved birth date, same tool, same day means the same seed string and therefore the same set. Readers with no birth date saved share a seed too, since theirs is built from the date and the tool name alone. Nothing about this is a collision or a fault; it is what a seeded generator does, and it is why you can check the result rather than take it on trust.
In principle, yes. The algorithm is public and tomorrow's seed is knowable today. These are picks for fun and they carry no information about any real draw, so there is nothing to protect.