CSV vs JSON vs XML: Which Format to Use (and How to Convert)
If you work with data at all, exporting a spreadsheet, pulling from an API, configuring software, you have met CSV, JSON and XML. They all describe structured data, but they were designed decades apart with different priorities, and picking the wrong one for the job creates more work than it saves.
CSV: flat and spreadsheet-friendly
CSV is the simplest of the three: rows separated by line breaks, fields separated by commas. It opens directly in Excel, Google Sheets, and every database import tool ever made. Its limitation is that it only handles flat, tabular data, there is no native way to represent nesting, like a customer with multiple addresses.
JSON: nested and developer-friendly
JSON represents data as nested objects and arrays, which makes it a natural fit for anything hierarchical. It is the de facto standard for web APIs today because it maps directly onto how programming languages represent data in memory. The downside: it does not open cleanly in a spreadsheet without flattening first.
XML: verbose but strict, and still everywhere in enterprise
XML predates JSON and is more verbose, every value wrapped in opening and closing tags, but it supports things JSON lacks natively: attributes, namespaces, and formal schema validation. That rigor is why XML never went away: banking feeds, government data, older enterprise software and many B2B exchanges still run on it.
Choosing the right format
- Flat, tabular data you will open in a spreadsheet: use CSV.
- Nested data going to or from a web API: use JSON.
- Data exchanged with an enterprise system or needing strict schema validation: use XML.
Converting between them, free and locally
In practice, most real work is getting data out of the format one system gives you and into the format the next system needs. All the conversion directions, CSV, JSON and XML each way, plus Excel in and out, run directly in your browser with your data processed locally rather than uploaded.
Questions
Frequently asked
Which format produces the smallest files?
JSON is usually most compact for nested data; CSV is smallest for flat tables. XML is the most verbose because of its closing tags.
Can nested JSON be converted to CSV?
Yes, though nested structures get flattened into dot-notated column names, since CSV has no native nesting.
Is my data uploaded when converting?
No. All conversions happen locally in your browser using JavaScript; your file is never sent to a server.