Jsony

JSON Formatter & Validator

Paste JSON to format and validate it. Everything runs in your browser — your data never leaves the page.

Indent
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Output

Formatted JSON will appear here.

What is Jsony's JSON Formatter & Validator?

Jsony is a fast, private JSON formatter and validator built for developers working with real-world API responses. Paste any JSON document, and Jsony will pretty-print it, validate its syntax, and let you explore its structure in a collapsible tree view — all without sending your data to a server.

The tool is built for handling JSON at scale. Paste a 50MB API response, and the parser runs in a Web Worker so the UI stays responsive while the structure renders progressively in a virtualized tree. Smart error messages point to the exact line and column where parsing failed, with a human-readable explanation rather than the cryptic Unexpected token at position 1247 you might be used to.

How to use it

  1. Paste or load JSON. Paste directly into the input pane (it auto-formats on paste), or click Open file to load a .json file from disk.
  2. See it formatted. The output pane shows your JSON either as an interactive collapsible tree (default) or as raw formatted text. Toggle between views without re-parsing.
  3. Filter with JSONPath. Type a query like $.users[*].email in the JSONPath bar to extract specific values. Results update live as you type.
  4. Adjust formatting. Pick your indent (2 spaces, 4 spaces, or tabs), enable sort keys for alphabetical ordering, or turn on tolerant parsing to allow trailing commas and // comments.
  5. Copy. Click Copy to put the formatted output (or your query result) on the clipboard.

Settings persist in your browser's localStorage between sessions, so once you've configured your preferences you won't have to set them again.

Common use cases

Inspecting API responses. Paste the response body from your API client and use the tree view to navigate nested structures. Search for specific values with JSONPath instead of scrolling through formatted text.

Debugging serialization issues.When your backend produces malformed JSON or your frontend can't parse what it received, paste the raw response. The line and column error pointer makes it obvious where the problem is.

Cleaning up minified JSON. A one-line minified payload becomes a readable, color-coded document instantly. Useful for code review, log forensics, or just understanding what an opaque request body actually contains.

Working with configuration files. package.json, tsconfig.json, deeply nested CI configs — open them, browse, search by key path. Sort keys alphabetically when you need to compare two configs side by side.

Extracting specific fields at scale. With a JSONPath query, pull every email, every id, or every nested metadata.tags[*] from a large document. The query runs against a parsed value cached in the worker, so iteration is instant once the document is loaded.

Frequently asked questions

Is my JSON private?
Yes. Everything runs in your browser. There's no server endpoint, no upload, no cookie, no analytics tracking your input. The complete source is open — see the GitHub link in the footer.
How big can my JSON be?
Multi-megabyte documents work smoothly. The tool has been tested with 50MB+ payloads and is designed around two specific bottlenecks: parsing runs in a Web Worker so the main thread isn't blocked, and the tree view uses virtualized rendering so only the rows you're looking at are painted.
Does it support comments and trailing commas?
Yes, with the 'Allow trailing commas & comments' setting turned on. By default, strict JSON is enforced so real errors aren't masked. Toggle the setting when you're working with JSONC or hand-edited config files.
What happens with invalid JSON?
Each parse error is shown with its exact line and column, the offending line of input, and a caret pointing at the column. The error message is human-readable — 'Missing comma between items' instead of the browser's default cryptic position-based error.
Is it free?
Yes. Jsony is free to use and the source is open under the MIT license.
Where can I report bugs or suggest features?
Open an issue on the GitHub repository (link in the footer). This is a personal project so there's no SLA, but bug reports with reproducible inputs are very welcome.

More tools coming soon

Jsony is a small set of focused, fast, privacy-respecting developer utilities. Coming next: a JSON Diff tool for comparing two documents, a JSON-to-CSV converter, a JWT decoder, and a Base64 encoder/decoder. All will follow the same principles: 100% client-side, fast on large inputs, clean UI without ads above the fold. See the home page for the current tool list.