How to Format JSON When Debugging API Responses

The first time you inspect a real API response in a network tab or a terminal, it usually looks like a single 2,000-character line: objects nested inside objects, no line breaks, no indentation. That's not a bug in your code — it's minified JSON, which servers send to save bandwidth. Before you can read the data, you need to format it: expand it into indented lines so each object, key, and value is visible.

What formatting actually does

Formatting (also called beautifying or pretty-printing) adds whitespace only — it changes nothing about the data itself. A formatter parses the JSON into a structure, then re-serializes it with indentation. Because it's a pure visual transformation, you can format and minify back and forth indefinitely without losing information. The one thing a formatter cannot do is fix invalid JSON: if the payload has a syntax error, there is nothing to parse, and formatting will only tell you where the error is.

A real example

Here is what a typical API response looks like straight off the wire:

• Raw: {"user":{"id":42,"name":"Ada","roles":["admin","billing"]},"meta":{"page":1,"total":137}}
• Formatted: the same data with each key on its own line, nested objects indented, and arrays split item-by-item so you can see at a glance that user.roles contains two values.

Once formatted, the structure is readable in seconds: the top-level keys, the shape of nested objects, and where arrays begin and end. That's usually enough to spot a missing field, an unexpected null, or a response wrapped one level deeper than your code expects.

The errors you'll actually meet

• Trailing commas — JSON forbids a comma after the last item in an object or array: {"a":1,} is invalid, even though many JavaScript tools tolerate it.
• Single quotes — JSON requires double quotes for keys and strings. {'name': 'Ada'} is valid JavaScript but invalid JSON.
• Unquoted keys — {name: "Ada"} works in JS, not in JSON.
• Trailing garbage — a stray comma, bracket, or second document after the closing brace makes the whole payload invalid.
• NaN or undefined values — these aren't representable in JSON and usually indicate a serialization bug on the server.

The debugging workflow

1. Copy the raw response body from the network tab, curl output, or logs.
2. Paste it into a JSON formatter — if it prints, your syntax is valid and you can read the structure.
3. If it refuses to format, read the error location and fix the reported character (usually a missing quote, extra comma, or truncation).
4. Compare two versions of a response with a diff tool when the payload changed between requests.