Fixed-Width ↔ CSV/JSON Converter

A fixed-width file has no separator: every field takes an exact number of characters and the leftover space is padded with blanks or zeros. Bank return files, mainframe extracts and the TXT many ERPs produce instead of a CSV all look like that, and a spreadsheet opens them as a single column. Describe the layout once, as name:14,state:2,amount:10, and get CSV, TSV or JSON out.

Widths mode adds fields up in order: 14 characters for the name, 2 for the state, 10 for the amount. Positions mode names the start and end of each field, so you can skip filler and read four fields out of a sixty-field layout. Automatic detection looks for character columns that are blank on every line and treats runs of two or more as separators, which is why it merges two fields parted by a single space.

Going the other way, the CSV becomes positional again: each field is padded to the declared width, with trailing spaces or leading zeros, the way numeric fields are usually written in transmission files. A value that does not fit is cut off, and the tool reports the line, the field and the original length. Finding that here beats finding it in the rejection report a day later.