If you've ever opened an API response or edited a config file, you've seen text full of curly braces. That's JSON. You don't have to be a developer to run into it while checking logs or handling data, and once you know the structure it's easier to read than it looks.
JSON is a shared grammar for writing data
JSON (JavaScript Object Notation) is a format for representing data as human-readable text. Think of it as a common language programs agree on when they exchange data. It's the de facto standard almost everywhere: web APIs, config files, communication between apps.
There are two basic building blocks.
- Object: a set of "name: value" pairs inside curly braces
{ }. It describes one thing. - Array: an ordered list of values inside square brackets
[ ]. Used when you have several of the same kind.
For example, a single user looks like this.
{
"name": "Jimin",
"age": 29,
"active": true,
"roles": ["editor", "reviewer"]
}
A name ("name") has a value ("Jimin"), age is a number, active is true/false, and roles is an array holding several values. There are only six value types: string, number, boolean, null, object, array, so the rules stay simple.
Common mistakes that stop the parser
JSON is strict. Errors that look trivial to a human make a program stop reading right at that spot.
- Trailing comma: you can't leave a comma after the last item in an array or object.
- Single quotes: strings and keys must be wrapped in double quotes
". Single quotes'are not allowed. - Unquoted keys:
{ name: "Jimin" }is wrong;{ "name": "Jimin" }is right. - Comments: JSON doesn't allow comments (
//) by the standard.
These are hard to spot by eye in a long payload, which is why it helps to have a formatter point to the line and column of the error.
Formatting and validation are different
The JSON you meet in practice is often minified onto one long line. Two jobs come up here.
Formatting makes it readable; validation checks that the syntax is correct.
Formatting indents along the hierarchy and colors the parts so the structure is visible at a glance. Validation checks for the syntax errors above. When you instead need to shrink the data, minifying strips all whitespace into a single line.
For sensitive data, keep it in the browser
JSON frequently carries sensitive values: tokens, personal data, internal identifiers. Some online tools send your input to a server to process it, so data you pasted without thinking can end up stored elsewhere. A tool that does everything inside your browser avoids that worry.
If you need to tidy JSON or find an error, paste it into the JSON Formatter. It adds indentation and syntax highlighting, points to the location of any error, supports one-line minifying, and never sends your input to a server.