I write small calculators for a Roblox fan-wiki as a side project, and the Bongo Cat drop-rate tool is the one where I almost shipped a number I couldn't actually back up. The naive version is easy: take the community-reported Legendary chest rate (roughly 1 in 500,000, since the developer has never published an official table) and divide it by 12, because there are 12 base-pool Legendary items, and print "1 in 41,666 chance of this specific hat." It reads clean. It's also fabricated precision, because nobody has published the individual weight on any of those 12 items, and averaging assumes they're evenly weighted, which is an assumption, not a fact.
So the tool only ever reports per-rarity-tier odds, never per-item. Common 90 percent, Uncommon 9.5 percent, Rare 0.49 percent, Epic 0.01 percent, Legendary about 1 in 500,000, as a tier, full stop. If a player wants a specific Legendary, the honest answer is "somewhere between 1 in 500,000 and 1 in 6,000,000 depending on how the game actually weights them, and nobody outside the dev team knows which end it's closer to." That's a worse-feeling answer than a clean percentage. It's also the true one.
The other thing I left alone on purpose: add up the five community-reported rarity percentages and you get roughly 100.0002 percent, not a clean 100. That's rounding noise from wherever the original community data was collected, not my error. I could silently normalize it to exactly 100 and nobody would notice. I didn't, because doing that would make the numbers look more precise than the source data actually is, and the entire point of the tool is not doing that.
Chest cadence is the third assumption I left exposed instead of hardcoding. The community estimate is roughly one chest per 30 minutes of active keyboard and mouse use, but the developer has never published the real cadence either, so the tool treats it as an editable input the player sets themselves rather than a baked-in constant.
None of this is complicated engineering. It's three small refusals: don't divide by an unknown weight distribution, don't silently normalize rounding noise, don't hardcode an unpublished rate as fact. The calculator itself is live at bongocat.wiki/tools/drop-rates if you want to see what "honestly uncertain" looks like as an actual UI instead of a caveat paragraph nobody reads.
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