JSON Viewer
Visualize JSON as an interactive collapsible tree. Click nodes to expand or collapse.
Inspect nested JSON without scanning every line
Large API responses, logs, and export files often contain objects inside arrays inside more objects. A JSON tree viewer lets you collapse whole branches and open only the field path you care about, instead of scrolling through a wall of formatted text.
Use it to inspect user objects, event payloads, feature flags, payment webhooks, analytics exports, and config files where the same key may appear at several nesting levels.
Tree view vs formatted text
Formatted JSON is best when you need to copy, edit, or compare text. Tree view is better when you need to understand structure: which fields are arrays, which fields are objects, and which values are strings, numbers, booleans, or null.
If the viewer cannot render the payload, validate the JSON first. If you find an array of similarly shaped objects and need to share it with a spreadsheet user, send it to JSON to CSV next.
Private browser-side viewing
The tree is built locally in your browser. FastDevTool does not upload the JSON, store your payload, or require an account.
That local workflow is useful for private API responses, staging data, customer-support examples, and data exports that should not leave your machine.
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Frequently Asked Questions
What is a JSON tree viewer?
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A JSON tree viewer renders JSON as an expandable/collapsible hierarchical tree, making it easy to navigate complex nested structures without reading raw text.
Can I collapse deeply nested nodes?
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Yes. Click any node's toggle arrow to collapse or expand it. Nodes deeper than 2 levels are collapsed by default to keep the initial view manageable.
What types does the viewer support?
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The viewer handles all JSON types: objects (shown with key count), arrays (shown with element count), strings (green), numbers (orange), booleans (blue), and null (gray).
When should I use JSON Viewer instead of JSON Formatter?
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Use JSON Formatter when you want readable text with indentation. Use JSON Viewer when the payload is deeply nested and you need to open one object, array, or field path at a time.
Does this JSON viewer work offline?
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Yes. FastDevTool is a Progressive Web App (PWA) with a service worker. Once you have visited the page, it works fully offline — no internet connection required.