Fixed-Width to JSON Converter - Parse Positional Data

Convert fixed-width text files to JSON format. Parse mainframe exports, COBOL data, and legacy reports. Define column positions, extract structured data.

Drop fixed-width file here or click to browse

Accepts .txt, .dat, .fix, .fw files

Sample Data (first line)

Load a file to see sample data...

Field Definitions

Define fields as name:start-end (1-based positions, inclusive)

Skip header row

Trim whitespace from fields

Auto-detect numbers

Skip empty lines

JSON Output

0 records

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Frequently Asked Questions

Fixed-width (positional) data uses character positions instead of delimiters to separate fields. Each column has a defined start position and length. Common in mainframe exports, COBOL systems, and legacy reports.

Enter field definitions as name:start-end pairs. For example, 'id:1-5,name:6-25,amount:26-35' defines three fields. Positions are 1-based and inclusive.

This tool uses simple position definitions. For complex COBOL copybooks with PIC clauses and nested structures, use our dedicated COBOL Copybook Parser tool.

The converter trims whitespace from both ends of each field by default. Toggle 'Preserve whitespace' to keep original padding for fields where spacing matters.

Enable 'Auto-detect numbers' to convert numeric-looking values to JSON numbers. Otherwise all fields become strings. Handles decimals, negatives, and leading zeros.

Check 'Skip header row' to ignore the first line. Useful when files include column labels that shouldn't be parsed as data.

For files with different record layouts (identified by a type code), process each record type separately with its own field definitions, or use the Record Type field to filter.

Output as JSON array (one object per record), or newline-delimited JSON (NDJSON) for streaming. Both formats are easy to process in any programming language.

Yes. All parsing happens in your browser using JavaScript. Your mainframe data and legacy files never leave your device.

The tool handles UTF-8 input. For EBCDIC mainframe files, first convert to ASCII using our EBCDIC to ASCII converter, then parse the fixed-width structure.

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