How to convert between Arabic and Roman numerals

1. Set the direction

   "Direction" picks `toRoman` (number → numeral) or `toArabic` (numeral → number). Pick once per run; both sides accept the appropriate format.

2. Enter the value

   "Value" is the number or numeral to convert. For `toRoman`, valid inputs are integers 1–3999 — beyond that, classical Roman numerals require overline notation which this tool doesn't emit. For `toArabic`, accepted letters are `I V X L C D M`; lowercase and uppercase both parse.

3. Press Run

   Result returns a single `result` field — the converted form. Examples: `2026` → `MMXXVI`; `MCMLXXXIV` → `1984`. Subtractive notation is used (`IV` for 4, `IX` for 9, `XL` for 40, `CD` for 400, `CM` for 900) — never `IIII` or `VIIII`.

4. Where the limit comes from

   Romans had no zero, no decimal places, and represented 5000+ with overlines on the same letters. This tool stops at 3999 (`MMMCMXCIX`) because anything higher needs that overline (or modern Unicode characters) and there's no canonical ASCII rendering.