CSV vs JSON vs Parquet vs Excel: Which to Use

Four formats cover most data work. Each is best at something different, and the wrong choice costs you time, space or accuracy.

Data moves between spreadsheets, apps, databases and analytics tools, and each one prefers a different file format. Picking the right one avoids slow imports, broken characters and files that are far larger than they need to be.

CSV is plain text with one row per line and a separator between values. Almost every tool can open it, and you can read it in a text editor. Its weakness is that it has no data types and no nesting. A date, a number and a ZIP code with a leading zero are all just text, so the program that opens it has to guess. Separators and text encodings also differ between countries, which is why a CSV sometimes opens as one long column. CSV is best for flat tables you want to share or import everywhere.

JSON stores data as objects and lists, so it can hold nested information such as an address inside a customer, or several phone numbers for one person. It keeps strings, numbers, true or false values and nulls apart. It is the standard format for web APIs. The cost is size: every key is repeated on every record, so a long table in JSON is much larger than the same table in CSV. JSON is best for API data and anything with a nested shape.

Parquet is a binary format made for analysis. It stores data by column, compresses it, and keeps the type of every column. Tools such as Spark, DuckDB, BigQuery and pandas read it very quickly, and a Parquet file is often several times smaller than the same CSV. You cannot open it in a text editor or in most spreadsheet programs. Parquet is best for large datasets you will query many times.

Excel (.xlsx) holds formatting, formulas, charts and several sheets, and it is what most business users expect. It is limited to 1,048,576 rows per sheet, it can quietly change values such as long numbers and dates, and it is a poor choice for automated pipelines. Excel is best for files that people will read and edit by hand.

A simple rule works well. Use CSV to exchange a flat table with anyone. Use JSON to send data to or from an API. Use Parquet to store and analyze big data. Use Excel to share with people who want to filter and format. Most real projects use two or three of them, so converting between formats is a daily task.

Open the Format Converter

Related tool pages

  • JSON to CSV Converter: Convert JSON to CSV online for free. Drop a file or paste data, click convert and download. It runs in your browser, so your data is never uploaded.
  • CSV to JSON Converter: Convert CSV to JSON online for free. Drop a file or paste data, click convert and download. It runs in your browser, so your data is never uploaded.
  • CSV to Parquet Converter: Convert CSV to Parquet online for free. Drop a file or paste data, click convert and download. It runs in your browser, so your data is never uploaded.
  • JSON to Parquet Converter: Convert JSON to Parquet online for free. Drop a file or paste data, click convert and download. It runs in your browser, so your data is never uploaded.
  • Parquet to CSV Converter: Convert Parquet to CSV online for free. Drop a file or paste data, click convert and download. It runs in your browser, so your data is never uploaded.
  • Parquet to JSON Converter: Convert Parquet to JSON online for free. Drop a file or paste data, click convert and download. It runs in your browser, so your data is never uploaded.

How to use the Format Converter: step by step

  1. Open the Format Converter.
  2. Choose the format you have and the one you need.
  3. Drop your file or paste the data.
  4. Click Convert, then copy or download the result.

When to use the Format Converter

  • Choose CSV for a flat export that must open anywhere
  • Choose JSON for API payloads and nested records
  • Choose Parquet for big datasets and fast analysis
  • Choose Excel for reports that people will edit

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: Converting a big CSV to Parquet usually shrinks it a lot and makes it faster to query. Convert back to CSV only when a person needs to read it.