How to Validate and Format JSON Before Using It in Your API

Working with APIs often means dealing with JSON. Most of the time, JSON is straightforward to read and write, but a small syntax mistake can make an otherwise correct API request fail.

A missing comma, an extra bracket, or an incorrectly quoted key can be enough to cause a parsing error.

Here are a few simple ways to validate and format JSON before using it in your application.

1. What Makes JSON Valid?

JSON has a relatively simple structure. Objects use curly brackets {}, arrays use square brackets [], and property names must be enclosed in double quotes.

For example:

{
"name": "John",
"age": 25,
"skills": ["JavaScript", "Python", "SQL"]
}

This is valid JSON.

A common mistake is using single quotes:

{
'name': 'John'
}

That's valid in some programming-language contexts, but it isn't valid JSON. JSON requires double quotes for strings and property names.

1. Check Commas and Brackets

Another common problem is a missing comma between properties.

Incorrect:

{
"name": "John"
"age": 25
}

Correct:

{
"name": "John",
"age": 25
}

The same applies to arrays and nested objects. When JSON becomes large, manually finding these mistakes can become frustrating.

1. Format JSON to Make It Readable

Minified JSON is useful when transferring data, but it isn't particularly comfortable to read:

{"name":"John","age":25,"skills":["JavaScript","Python"]}

Pretty-printed JSON is much easier to inspect:

{
"name": "John",
"age": 25,
"skills": [
"JavaScript",
"Python"
]
}

Formatting doesn't change the actual data. It simply makes the structure easier to understand.

For quick checks while working with API responses or configuration files, I use a browser-based JSON Formatter to format and inspect JSON without setting up another development environment.

1. Validate JSON Before Sending an API Request

If you're working with JavaScript, JSON can also be validated programmatically.

For example:

const jsonString = {
"name": "John",
"age": 25
};

try {
const data = JSON.parse(jsonString);
console.log("Valid JSON:", data);
} catch (error) {
console.error("Invalid JSON:", error.message);
}

JSON.parse() attempts to convert the JSON string into a JavaScript object.

If the JSON is invalid, JavaScript throws an error that you can catch and handle.

1. Don't Confuse JSON With JavaScript Objects

This is another common source of confusion.

A JavaScript object can look like this:

const user = {
name: "John",
age: 25
};

JSON representation would be:

{
"name": "John",
"age": 25
}

They look similar, but they're not exactly the same thing.

JSON is a data-interchange format with stricter syntax rules.

1. A Simple JSON Debugging Workflow

When an API request fails because of a JSON-related error, I generally check things in this order:

Check whether all brackets are closed.
Check commas between properties.
Make sure property names use double quotes.
Check string values for incorrect quotes.
Check nested objects and arrays.
Parse the JSON to see whether the syntax is valid.
Format the JSON so the structure is easier to inspect.

This simple checklist catches many common problems before they turn into longer debugging sessions.

Conclusion

JSON itself isn't complicated, but small syntax mistakes can be difficult to spot when you're working with large payloads.

Formatting and validating JSON before sending an API request can make debugging considerably easier. Whether you're working on a REST API, configuration file, frontend application, or backend service, keeping your JSON readable and valid is a useful habit.

For quick browser-based formatting and inspection, you can use the Allyoutools JSON Formatter.