About octal and binary

Octal is base 8, using digits 0–7. Each octal digit maps to exactly three bits, which is why Unix file permissions like 755 are octal. Code writes it with a 0o prefix.

Binary is base 2 — every digit is a bit, 0 or 1. It's what hardware actually stores, and it surfaces anywhere bit flags, masks, or permissions do. Code usually writes it with a 0b prefix.

For example, octal 755 is 111101101 in binary. The converter uses BigInt, so numbers of any size convert without losing precision — and it all runs in your browser.