What is JSON Formatting?
JSON formatting (pretty-printing) rewrites a valid document with consistent indentation and line breaks so nested objects and arrays are readable. It does not change string values or numbers — only insignificant whitespace between tokens. Minified JSON such as {"user":[{"id":1}]} becomes a multi-line structure you can scan in a code review or while debugging an API response.
SparkJSON also validates while it formats. Invalid input — for example an unquoted key like {name: "Ada"}, or a trailing comma before } — fails with an exact line and column instead of a generic "Unexpected token" from JSON.parse alone.
Is My JSON Data Secure on SparkJSON?
Yes for privacy of the paste itself: SparkJSON is 100% client-side. Your JSON is not uploaded to our servers, not written to a database, and not logged by an application backend — because there is no tool backend that receives input. Formatting runs in the page (and a Web Worker for large files). You can verify this in DevTools → Network while you paste production-like data.
Hosting still serves static assets (HTML, JS, CSS). That is unrelated to your editor contents. Treat irreplaceable secrets with the same caution you would on any website, and prefer a local editor when policy requires air-gapped handling.
How to Format and Validate JSON Online
- Paste JSON into the input panel, or use Upload for a local
.jsonfile. - Choose indent size (2 spaces, 4 spaces, or tabs).
- Click Format & Validate (or press Ctrl + Enter / ⌘ + Enter).
- Read the status: Valid JSON, or an Invalid message with line and column — fix that spot and run again.
- Optionally Compress (minify), Sort Keys, Copy, or Download the result.
Frequently Asked Questions
Does SparkJSON upload my JSON to a server?
No. Parsing and formatting run in your browser (including a Web Worker for larger files). There is no API that receives your paste. Confirm in DevTools → Network while you work.
Why does SparkJSON reject a trailing comma?
Strict JSON (RFC 8259) does not allow trailing commas. {"a": 1,} is invalid even though JavaScript object literals allow it. Remove the comma before } or ] and validate again.
What does the duplicate-key warning mean?
If an object defines the same key twice — for example {"id": 1, "id": 2} — most engines (including JSON.parse) keep only the last value. SparkJSON warns so you do not lose data silently.
Can I format large JSON files without freezing the tab?
Yes. Heavy work runs off the main thread in a Web Worker. Extremely deep nesting (beyond about 1,000 levels) is rejected with a clear error instead of crashing the tab.