Free Online Data Conversion Tools: What to Use for Each Job
There are four kinds of free tools for converting data files. Each is the right choice for a different job, so here is how to pick one quickly.
Before choosing, answer four questions. Can the file leave your computer? How big is it? Which formats do you need (Parquet is the one many tools miss)? And must numbers, dates and codes like 00123 survive the conversion unchanged?
Spreadsheet apps such as Excel and Google Sheets open CSV and Excel files and save them as CSV. Excel can also import JSON through Get Data (Power Query). They are good for a quick look and small edits, but they do not save Parquet, and opening a CSV in a spreadsheet can silently change data: leading zeros are dropped and long numbers are rounded.
Code is the best choice for repeatable work. pandas, Polars and DuckDB read and write CSV, JSON, Parquet and Excel. In DuckDB one line converts a CSV to Parquet: COPY (SELECT * FROM 'data.csv') TO 'data.parquet' (FORMAT PARQUET). The cost is installing Python or DuckDB and writing the script.
Upload-based online converters need nothing installed: you send the file to a website and download the result. That is convenient for public data, but the file goes to someone else's server, many sites limit file size, and some ask for an account for larger files. Read the privacy terms before you upload customer or financial data.
Browser-based tools do the conversion in your browser, so the file stays on your device and there is nothing to install. The limit is your device's memory rather than an upload size. Data Utility works this way: the Format Converter turns CSV, JSON, Excel and Parquet into each other, keeps types and leading zeros, flattens nested JSON, and also works offline once installed as an app.
Be clear about the limits too. Data Utility does not convert XML to JSON or format SQL, and very large files depend on how much memory your browser has. For those jobs, or for a pipeline that runs every night, a script is the better tool.
A simple rule: use a spreadsheet to look at data, a browser-based converter for one-off conversions of private files, an upload-based converter only for public data, and code when the same conversion has to run again and again.
Related tool pages
- JSON to CSV Converter: Convert JSON to CSV in seconds. Drop a file or paste data and download the result. Private: it runs in your browser and nothing is uploaded. Large files too.
- CSV to JSON Converter: Convert CSV to JSON in seconds. Drop a file or paste data and download the result. Private: it runs in your browser and nothing is uploaded. Large files too.
- CSV to Parquet Converter: Convert CSV to Parquet in seconds. Drop a file or paste data and download the result. Private: it runs in your browser and nothing is uploaded. Large files too.
- JSON to Parquet Converter: Convert JSON to Parquet in seconds. Drop a file or paste data and download the result. Private: it runs in your browser and nothing is uploaded.
- Parquet to CSV Converter: Convert Parquet to CSV in seconds. Drop a file or paste data and download the result. Private: it runs in your browser and nothing is uploaded. Large files too.
- Parquet to JSON Converter: Convert Parquet to JSON in seconds. Drop a file and download the result. Private: it runs in your browser and nothing is uploaded. Large files too.
How to use the Format Converter: step by step
- Open the Format Converter.
- Drop your CSV, JSON, Excel or Parquet file.
- Choose the output format and check the preview.
- Download the converted file. Nothing is uploaded.
When to use the Format Converter
- Convert a customer export to Parquet without uploading it
- Turn a JSON API response into a CSV for a spreadsheet
- Save an Excel sheet as JSON for an app
- Check which tool keeps leading zeros and dates intact
Example
Input: id,name,age 1,Ada,36 2,Alan,41
Output: [{"id":1,"name":"Ada","age":36},{"id":2,"name":"Alan","age":41}]
Frequently asked questions
How big can a file be?
It depends on your device. A few hundred MB usually works.
Which conversions does the Format Converter support?
Any direction between JSON, CSV, Parquet and Excel (.xlsx), for one file or a whole folder. Nested JSON is flattened into columns such as address.city. For Excel, the first sheet is read; old .xls files are not supported.
Why did my number or date change after converting?
Types are detected from the values. Turn off "Detect types" to keep everything as text, which also keeps leading zeros in IDs and phone numbers.
Tip: Test a converter with a file that has a leading-zero code (00123) and a date. If either changes, pick another tool.