Base Number Converter

Type a number into any of the four fields — Binary, Octal, Decimal, or Hexadecimal — and the other three convert and fill in instantly using the same underlying value. Each field shows a hint like “Digits 0–7 only” so you know which characters are valid before you type. If you type a character that’s invalid for that base — like a “9” in the Binary field — it’s flagged with an error message immediately, and the other three fields keep showing your last valid conversion instead of clearing.