JSON File Format (.json)
A JSON file holds data as nested objects and arrays built from strings, numbers, booleans and null, and nothing else, written in the syntax JavaScript uses for object literals.
JSON at a glance#
| Full name | JavaScript Object Notation |
|---|---|
| File extension | .json |
| Category | Data Files |
| Developer | Douglas Crockford |
| First released | 2001 |
| MIME types | application/json |
| Compression | Uncompressed |
| Specification | RFC 8259 |
| FileFlip support | FileFlip reads and writes this format |
What a .json file can hold#
These are the things a JSON file either supports or does not, and they are what decides whether a conversion keeps everything or quietly drops something.
| Human readable | Yes |
|---|---|
| Comments | No |
| Schema or validation | Yes |
Strengths and limitations of JSON#
What JSON does well
- Parses natively in every browser and nearly every language's standard library
- The grammar is small enough that independent parsers rarely disagree on how to read a file
- Nesting objects and arrays to arbitrary depth costs nothing extra in the syntax
Where JSON falls short
- No comment syntax, so a JSON config file can't explain any of its own values
- A trailing comma after the last item is a syntax error, not a style choice
- No date or time type, so timestamps travel as strings or numbers by convention alone
- Object key order isn't guaranteed by the spec, even though most parsers preserve it
Reach for JSON when data moves between programs and nobody needs to hand-edit it, since every language parses it the same way.
Convert JSON to YAML or TOML when a person needs to edit the file directly and wants comments, or to CSV when a spreadsheet or a script expecting rows is the destination.
How to open a .json file#
A .json file opens in the programs below, grouped by the platform you are on. If you would rather not install anything, FileFlip converts JSON into a format your machine already opens, and it does it in the browser tab rather than on a server.
| Platform | Programs that open it |
|---|---|
| Windows | VS Code, Notepad++, Sublime Text |
| macOS | VS Code, Sublime Text, TextEdit |
| Linux | VS Code, vim, gedit |
| Web | FileFlip |
JSON questions people ask#
Why doesn't JSON support comments?
JSON has no comment syntax by design. Douglas Crockford, who specified JSON, has said he removed comments deliberately after seeing people use them to hold parsing directives that broke interoperability between tools. A config file written in JSON that needs to explain itself either adds a plain key like _comment by convention, or moves to a JSON superset like JSON5 or JSONC, which aren't plain JSON.
What happens when I convert a JSON array of objects to CSV?
Converting JSON to CSV only works cleanly when the JSON is a flat array of objects sharing the same keys, because CSV has no way to represent nesting. A nested object or array inside a field gets flattened with a naming convention like address.city, stringified as JSON text inside one cell, or dropped, depending on which tool is doing the conversion.
Does JSON have a date type?
No, JSON has no date or time type. Dates in JSON files are always strings, most often ISO 8601 like 2026-08-26, or Unix timestamps written as numbers, and which convention a given API uses is something you have to check rather than infer from the format itself.
What happens to a JSON object when I convert it to XML?
A JSON object's keys become XML elements when converted to XML, since JSON has no equivalent of an XML attribute and the converter has to pick elements for everything. A JSON array needs a wrapper element plus a repeated child element to become valid XML, both of which JSON's own syntax never required.
Converting JSON files#
Convert JSON to another format
Convert another format to JSON
Every conversion runs inside your browser. The file is read from your disk, the work happens on your own machine, and nothing is uploaded. How FileFlip works names the engine behind each family and how to verify that for yourself.