Withdata DataFileConverter merges fixedwidth files into one JSON file locally — any number of files, mapped column by column, with the output options of your choice. 100% local, secure, and cross-platform.

Why Choose Withdata DataFileConverter as a Fixed-Width Text Merger?

🔒 100% Local & Secure

All merging runs on your own computer. Nothing is uploaded to any cloud server.

⚡ Fast Streaming Merge

Millions of rows within a minute. Large files are streamed with low memory usage.

📁 Any Number of Files

Add two files or a whole folder, then combine everything into a single JSON file.

🔄 Column Mapping

Files with a different column order or extra columns can be mapped to the output columns before merging.

🖥 Windows, macOS, Linux

Native builds for Windows, macOS and Linux, with a step-by-step GUI wizard and a command line interface.

⏱ CLI & Scheduled Tasks

Save a merge session and run it automatically from Windows Task Scheduler or crontab.

Full Feature Comparison

Feature	Supported details
Input	Any number of Fixed-Width Text files, added one by one or as a folder
Output format	JSON object array, plain JSON array, or JSON Lines (one object per line)
Merge mode	All input rows into one output file
Running mode	GUI wizard · command line · scheduled tasks
Column handling	Source columns are mapped to the output columns
Output options	Object array / plain array / JSON Lines, date format
Platform	Windows, macOS, Linux (native, 64-bit)

Fixed-Width Text to JSON — What Changes

Each fixed-width line becomes a JSON object, keyed by the column names you defined. Every value starts as a string, because a fixed-width column has no type.

All Fixed-Width Text Merge Options You Need

Merge several Fixed-Width Text files into one JSON file — step by step in the GUI wizard
Merge a whole folder of Fixed-Width Text files in one run
Map the columns of each input file to the output columns
Run the merge from the command line, and schedule it as a scheduled task
All Fixed-Width Text tools and all JSON tools

Same source format, other targets

This page merges Fixed-Width Text into another format. If you need a different output, these pages each do that one job:

All merge tools, by format

Merging into JSON — Notes

Nested objects are flattened into dotted column names when the files are read.
There is no delimiter and no quoting — every column has a fixed width.
Merged output widths are measured from the data (widest value plus 15% slack, at least 2 and at most 15 extra characters) and can be edited.
For N columns, N-1 widths are used — the last column takes the rest of the line.
When reading fixed-width files: N columns need N-1 widths, no delimiter is used, and the header row is optional.

How to Merge Fixed-Width Text Files (4 Steps)

Open Withdata DataFileConverter and choose Merge (combine multiple files into one).
Add the Fixed-Width Text files you want to merge — two files, a list, or a whole folder.
Check the preview and map the source columns to the output columns; then set the output options (Object array / plain array / JSON Lines, date format).
Click Convert — the single JSON file is written in seconds. Save the session if you want to run it again from the command line.