Speciedle is a free daily guessing game about the animal kingdom. Each day there's one mystery animal species, and you close in on it by guessing other animals. Every guess is scored by how closely related your guessed animal is to the hidden animal.
The idea
Most guessing games measure closeness by letters or by meaning. Speciedle measures it by evolutionary relatedness. We are choosing to use how long ago your guess and the mystery species last shared a common ancestor as our relatedness metric. Guess a lion when the answer is a housecat and you'll score high, because cats branched apart recently. Guess a jellyfish and you'll be way out on a distant limb of the tree of life.
I built it because that gradient turns out to be a genuinely fun thing to climb. You start
with a wild stab, watch the shared clade narrow from Mammalia (mammals) to
Carnivora (carnivores) to Felidae (cats), and feel yourself
homing in. Along the way you pick up a surprising amount about how animals are actually
related to one another.
An early version scored guesses on raw DNA similarity — the "humans and chimps share 98% of their DNA" idea. It didn't work as a game: sequence similarity flattens out past a few hundred million years, so most of the animal kingdom ended up bunched at the same score. Divergence time, millions of years since a shared ancestor, gives a clean gradient across the whole tree, so that's what Speciedle uses.
Who it's for
Anyone who likes a quick daily puzzle, and anyone who's a little bit curious about the natural world. You don't need to know any taxonomy to play — the game teaches you as you go, and every clade name has a one-tap definition. Bring a guess, follow the hints, and you'll get there.
Where the data comes from
Speciedle stands on a lot of freely available science and open data:
- Taxonomy (the tree's shape): NCBI Taxonomy, which is in the public domain. It decides which clades nest inside which.
- Clade ages (the scoring): hand-curated from TimeTree and the primary scientific literature. These are game calibration points chosen to feel right, not research-grade figures — if a date looks slightly off to an expert eye, that's why.
- Species photos: from Wikimedia Commons, each shown with its photographer and licence (typically Creative Commons BY or BY-SA). Hover or tap any animal to see its credit.
Huge thanks to the people and projects behind all of the above. A guessing game like this simply couldn't exist without open data and freely licensed photography.
An indie project
Speciedle is a small, independent, one-person project — no company, no venture funding, no sign-up. It's free to play, and it's kept running with a little help from ads on the page. There are no accounts and nothing to install; your stats and streaks live only in your own browser.
Got a favourite animal that's missing, spotted a wrong-looking score, or just want to say hi? Head to the Contact page — I'd love to hear from you.