Withdata DataFileConverter merges CSV files into one yaml 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 CSV 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 YAML 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 CSV files, added one by one or as a folder
Output format	YAML with configurable indent (2 spaces by default) and flow style
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	Indent (2 spaces by default), flow style, nested mappings
Platform	Windows, macOS, Linux (native, 64-bit)

CSV to YAML — What Changes

The merged rows are written as one YAML mapping each, with the CSV header cells as the mapping keys. The indent is two spaces by default, and a header cell that contains a dot is written back as a nested mapping.

All CSV Merge Options You Need

Merge several CSV files into one YAML file — step by step in the GUI wizard
Merge a whole folder of CSV 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 CSV tools and all YAML tools

Same source format, other targets

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

All merge tools, by format

Merging into YAML — Notes

Each merged row is written as one mapping in a top-level YAML sequence.
The output indent is 2 spaces by default and can be changed; flow style ({ } / [ ]) can be toggled.
Column names that contain dots (for example address.city) can be written back as nested mappings.
When reading YAML: a top-level sequence of mappings is one row per mapping, nested mappings become dotted column names, and anchors/aliases/tags/multi-document files are not supported.
The delimiter and quote character can be chosen; quoted fields and embedded line breaks are parsed correctly.

How to Merge CSV Files (4 Steps)

Open Withdata DataFileConverter and choose Merge (combine multiple files into one).
Add the CSV 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 (Indent (2 spaces by default), flow style, nested mappings).
Click Convert — the single YAML file is written in seconds. Save the session if you want to run it again from the command line.