Does it handle Russian gender and plural rules?

Yes. It uses одна/две for the feminine тысяча, and picks the right plural form — тысяча, тысячи or тысяч — based on the standard Russian 1 / 2-4 / 5+ agreement rule.

How large a number can I convert?

Up to 12 digits in the integer part, which covers values into the billions (миллиарды).

Is anything sent to a server?

No. The conversion runs entirely in your browser — no number you type ever leaves your device.

Number to Words in Russian

Spell any number in Russian words — instantly, in your browser.

Number to words in Russian

Type any whole number and see it spelled out in Russian words, with the correct grammatical gender and plural agreement applied automatically — for example одна тысяча, две тысячи, and пять тысяч.

Everything happens in your browser. Nothing you type is uploaded anywhere.