Where this comes in handy
Spelling a number out in words is required on cheques, legal documents, and some formal contracts, and it's also useful for proofreading - style guides often call for spelling out numbers under a hundred in running text. This converts whole numbers up into the trillions, negative numbers, and simple decimals, read out digit by digit after the word "point."
How large numbers get broken down
The converter processes a number in groups of three digits at a time - ones/tens/hundreds, then thousands, then millions, then billions, then trillions - converting each group to words and attaching the right scale word, exactly the way you'd naturally read a large number out loud: "fourteen million, two hundred thousand," for example, rather than reading every digit individually.
Why there's a dedicated Currency / cheque format
Writing "twelve point five zero" on a cheque wouldn't be accepted - banks expect a specific convention: the whole-number part spelled out, followed by the currency name, "and," the decimal part spelled out as its own whole number of cents (or pence, or paise), the minor unit name, and the word "Only" at the end to block anyone from adding extra digits. Switching the Format dropdown to "Currency / cheque format" produces exactly that - for example, 1234.5 becomes "One Thousand Two Hundred Thirty-Four Dollars and Fifty Cents Only" rather than the plain-number reading.
How decimals are handled differently from the whole-number part
The portion before the decimal point is converted using the full number-naming logic described above, but the portion after the decimal point is read digit-by-digit instead - 12.5 becomes "twelve point five," and 12.50 becomes "twelve point five zero," matching how decimals are conventionally read aloud (rather than treating ".50" as its own two-digit number, "fifty").
Common uses
Writing out a cheque amount in words to match the numeral, double-checking a legal or formal document's written-out number matches the numeral elsewhere in the text, or simply converting a number for a worksheet, quiz, or language-learning exercise.