JSON, XML and CSV each solve a different problem. Here is how to pick the right one, plus tools to convert and validate between them.

Whenever data needs to move between systems, export from a spreadsheet, or get sent to an API, it has to be structured in some format. JSON, XML and CSV are the three you will run into most often, and each one is a genuinely different tradeoff, not just a stylistic choice.

CSV: simple, tabular, everywhere

CSV (comma-separated values) is plain text organized into rows and columns, exactly like a spreadsheet. It is the easiest format for humans to read and for spreadsheet software to open directly. Its limitation is structure: CSV handles flat, table-shaped data well, but has no good way to represent nested or hierarchical information, like an order that contains a list of line items, each with its own set of properties.

JSON: the web's default

JSON (JavaScript Object Notation) represents data as nested objects and arrays with key-value pairs. It naturally handles hierarchy, which CSV cannot, and it is compact and fast to parse. This is why it is the default format for nearly every modern web API. Its main tradeoff compared to CSV is that it is less convenient to open and skim in a spreadsheet, since it is not naturally tabular.

XML: verbose, but strict

XML (eXtensible Markup Language) also handles nested, hierarchical data, using opening and closing tags similar to HTML. It predates JSON and is more verbose, but it has mature support for strict schemas (defining exactly what structure a document must follow) and namespaces, which is why it is still standard in enterprise systems, older APIs, and some document formats like RSS feeds and SOAP web services.

Which one should you use?

• Exporting data for a spreadsheet, or working with simple tabular data: CSV.
• Building or consuming a modern web API, or config files for a JavaScript project: JSON.
• Working with a legacy enterprise system, or a format that specifically requires it, like RSS: XML.

In practice, you often do not get to choose; the system you are integrating with dictates the format, and the real task is converting cleanly between whatever you have and whatever you need.

Converting between formats

SEOpeck has dedicated converters for every direction: CSV to JSON, JSON to CSV, JSON to XML and XML to JSON. Before sending JSON anywhere, it is worth running it through the JSON Validator to catch a trailing comma or missing bracket before it causes a failure downstream, and the JSON Beautifier makes minified, single-line JSON readable again when you need to inspect it by eye.