Fixed Width ↔ CSV Converter

A fixed-width (or positional) file is a text file where each field in a record occupies a fixed number of characters. There are no delimiters between fields — the position and length of each field define its boundaries. For example, characters 1-10 might be an account number, 11-40 a name, and 41-52 a balance. This format is common in mainframe systems, COBOL programs, banking files (NACHA/ACH), government data feeds, and EDI transactions.

The auto-detect algorithm scans all lines in your input and counts how many lines have a space at each character position. Positions where a high percentage of lines (70% or more) have spaces are identified as potential column boundaries. The tool then groups consecutive space positions into gaps and uses the transitions between gaps and non-gaps to define column start positions and widths.

Yes. Each column definition includes an alignment option (left or right). For numeric fields that are right-justified with leading spaces or zeros, set the alignment to 'right'. When converting CSV to fixed-width, the tool will pad the value on the left side. When converting fixed-width to CSV with trim enabled, leading spaces or zeros are removed.

When converting CSV to fixed-width, you can choose between space padding (the default) and zero padding. Space padding is standard for text fields, while zero padding is common for numeric fields in financial file formats like NACHA/ACH files.

Yes. All parsing and conversion runs entirely in your browser using JavaScript. No data is sent to any server. You can verify this by checking the Network tab in your browser's developer tools while using the tool. This makes it safe to use with sensitive financial, medical, or proprietary data.

Fixed-width files typically do not have a CSV-style header row. Instead, the column structure is defined externally (e.g., in a copybook or specification document). In this tool, you define column names in the Column Definitions panel. When converting fixed-width to CSV, the tool automatically adds a header row using your column names. When converting CSV to fixed-width, the header row from the CSV is used to map columns.

The presets provide common fixed-width layouts with sample data so you can quickly see how the tool works. The COBOL Copybook preset uses a typical mainframe record layout, the Bank Statement preset mimics financial statement formats, and the Log File preset shows server log parsing. Click any preset to load its column definitions and sample data.