Raw JSON from an API response is nearly unreadable. A 500-line JSON object on a single line, with no indentation and no syntax highlighting, is hostile to human eyes. You need to find one field in a response that might contain dozens of nested objects and arrays. Without a proper viewer, this means copying the JSON, pasting it into a formatter, visually scanning the formatted output, and repeating the process every time the response changes.
A JSON viewer that parses, formats, syntax-highlights, and lets you collapse and expand sections transforms API debugging from an exercise in frustration to something manageable.
What a good JSON viewer does
Formatting. Takes minified JSON and adds proper indentation. This is the minimum bar -- most tools do this.
Syntax highlighting. Colors strings differently from numbers, booleans, nulls, and keys. Makes the structure scannable at a glance.
Collapsible sections. In a large JSON response, you want to collapse the sections you do not care about and expand the ones you do. A tree view where you can click to expand or collapse objects and arrays is essential for responses with more than 50 lines.
Search. Find a specific key or value without scrolling through thousands of lines. Search should match keys and values separately and highlight all occurrences.
Path display. When you click on a value, show the full access path (e.g., response.data.users[0].email). This is the path you need in your code to access that value.
Validation. When you paste invalid JSON, show the exact position of the syntax error. A missing comma on line 47 is much easier to fix when the tool highlights line 47 than when it says "Unexpected token."
Common JSON problems
Trailing commas. Valid in JavaScript, invalid in JSON. The object {"a": 1, "b": 2,} fails to parse. This is the most common "why won't it parse" issue.
Single quotes. JSON requires double quotes. {'key': 'value'} is invalid. JavaScript allows both; JSON does not.
Unquoted keys. {key: "value"} is valid JavaScript but invalid JSON. Keys must be quoted strings.
Comments. JSON does not support comments. // this is not valid in a JSON file causes a parse error. JSON5 and JSONC (JSON with Comments) are extensions that support comments, but standard JSON does not.
Numeric precision. JSON numbers are IEEE 754 floating-point. Large integers (above 2^53) lose precision when parsed in JavaScript:
JSON.parse('{"id": 9007199254740993}')
// {id: 9007199254740992} -- last digit changed!
This is a real issue with Twitter/X API tweet IDs and other services that use large integer identifiers.
JSON in the developer workflow
JSON is everywhere: API responses, configuration files, log entries, database documents, message queues, and state management. Being able to quickly parse, view, and navigate JSON is as fundamental as reading code.
In the terminal:
# Pretty-print with jq
curl https://api.example.com/data | jq '.'
# Extract specific fields
curl https://api.example.com/users | jq '.[0].name'
# Filter by condition
curl https://api.example.com/items | jq '.[] | select(.price > 50)'
In the browser DevTools, the Network tab automatically formats JSON responses. But when you have JSON from other sources -- log files, clipboard, message queues -- you need a standalone viewer.
I built a JSON viewer at zovo.one/free-tools/json-viewer with collapsible tree navigation, syntax highlighting, search, path display, and validation with error location highlighting. Paste any JSON -- from API responses, config files, or log entries -- and navigate it visually. Faster than squinting at raw text.
I'm Michael Lip. I build free developer tools at zovo.one. 500+ tools, all private, all free.
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