About MostlyOdd
MostlyOdd is an independent, advertising-supported site about the strange-but-true — odd history, famous hoaxes, bizarre disappearances, and the odd corners of science and the natural world. Alongside the articles, we built six free tools that let you check the numbers and browse the record books yourself instead of taking a claim’s word for it. Here is what each one actually does.
The odds tools
Two of the tools are pure math. The Coincidence Probability Calculator runs the birthday-paradox math for any group size, or works out the chance that at least one of several independent 1-in-X events happens, and shows the result both as a percentage and as a plain “1 in X” figure. The Oddity Probability Calculator runs the other direction: give it odds like “1 in 15,000” and it converts them into a probability, the number of times you’d expect that to happen across a population you choose, and a plain-language comparison to other genuinely documented long odds — a lightning strike, a lottery jackpot, a royal flush, a shark encounter, a four-leaf clover. Both tools use standard probability formulas; neither one invents its comparison figures.
The collections you can browse
The other four tools are curated, filterable collections rather than calculators. The Weird Science Fact Generator steps through a hand-checked set of true, strange facts across space, biology, physics, and the human body, with a one-line explanation of why each one is true and a filter by field. The Strange Phenomenon Analyzer covers real, documented natural and atmospheric phenomena — ball lightning, the Brocken spectre, sailing stones, Morning Glory clouds — filterable by type and by whether science currently calls each one explained or still debated. The Bizarre World Record Tracker lets you filter and sort genuinely documented world records, from the longest recorded attack of hiccups to the largest ball of twine, by category or by year. And the Unusual Animal Trait Identifier catalogs real animals with genuinely strange biology — the immortal jellyfish’s biological immortality, the tardigrade’s cryptobiosis, the mantis shrimp’s sixteen photoreceptors, the axolotl’s limb regeneration — searchable by trait or by species.
The Cabinet of Curiosities
If you’d rather browse than calculate, the Cabinet of Curiosities is a gallery of strange artifacts, famous hoaxes, forgotten inventions, and the sites of unsolved mysteries. Every entry, image, and fact in it is drawn from Wikipedia and Wikimedia Commons; we are not affiliated with either project, and each entry links back to its source rather than claiming the material as our own.
What this is (and isn’t)
MostlyOdd is independently run and supported by advertising, which is how the tools, the articles, and the museum stay free with no registration required. The tool outputs are general-interest estimates built on standard math and documented figures — not medical, scientific, legal, or safety advice, and not a substitute for checking a primary source when something actually matters. Folklore, cryptid, and paranormal subjects that come up in our articles are presented as cultural history and legend, not as established fact. For more of the same kind of strange-but-true reading, the blog and learn section are where we keep digging; questions, tips, and corrections are always welcome on the contact page.