About PerfectJSON: JSON Validator & Formatter
PerfectJSON is a fast, free JSON formatter, validator and editor that treats your data the way it should be treated: it never sees it. Everything is processed in your browser and never uploaded.
Jump to: Features · Why we built it · Privacy Policy · Terms of Use · FAQ · Contact
Private JSON validation that runs in your browser
Most online JSON tools send your document to a server to format or validate it. PerfectJSON has no server to send anything to. The whole application is static files, and every feature (parsing, validation, formatting, diffing, conversion) runs as JavaScript on your own machine. Your JSON is never uploaded, logged or stored anywhere but your device, which makes it safe for API payloads, access tokens, configuration files and anything else you would not want to paste into a stranger's server.
The website itself uses standard analytics and displays ads to cover its running costs (both described in the privacy policy). Neither ever receives the contents of the JSON you edit — that stays local.
JSON formatting, validation, editing and conversion features
PerfectJSON bundles the tools a developer reaches for when working with JSON into a single page, with no round trips to a server.
JSON formatter and beautifier
Pretty-print messy JSON with your choice of indentation, or minify it to a single line to shrink a payload. Syntax highlighting makes structure obvious at a glance.
JSON validator with detailed error messages
Validate against RFC 8259, RFC 7159, RFC 4627 or ECMA-404. Instead of a vague "invalid JSON", PerfectJSON reports the exact line and column, explains what it expected, and highlights the offending range in the text. It keeps parsing past the first error so you can fix several problems in one pass.
JSON tree view editor
Edit JSON visually in a tree or table view: click any key or value to change it, toggle booleans, pick colors for color strings, and add or delete entries without hand-balancing brackets. Prefer raw text? Edit it directly with live highlighting.
JSON diff tool
Compare two documents with a side-by-side JSON diff viewer to see exactly which lines were added, removed or changed between versions of a config or an API response.
JSON converter and export tools
Convert JSON to YAML, CSV, plain text, formatted JSON or minified JSON, and copy the result or download it as a file.
Lossless JSON editing
PerfectJSON preserves large numbers and 64-bit IDs without JavaScript's precision issues. Standard parsers round integers above 9007199254740991, silently corrupting database IDs; PerfectJSON detects them and keeps every digit intact through formatting and editing.
- Format, beautify and minify JSON with configurable indentation.
- Validate JSON against RFC 8259, RFC 7159, RFC 4627 and ECMA-404 with line- and column-precise errors.
- Auto-fix trailing commas, single quotes, unquoted keys, comments and unbalanced brackets in one click.
- Edit JSON in a tree or table view, or as raw highlighted text.
- Compare JSON files with a side-by-side JSON diff viewer.
- Convert JSON to YAML, CSV, plain text, formatted JSON or minified JSON.
- Preserve large numbers and 64-bit IDs with a lossless parser.
- Share a document as a link, switch between dark and light mode, and undo any change.
Built for developers
PerfectJSON started as a privacy-focused alternative to the many online JSON tools that quietly upload your data to format it. The goal is simple: a fast, capable JSON editor that never asks you to trade away privacy to use it. If you have ever hesitated before pasting a production API response into a random website, this was built for you.
How PerfectJSON is built
PerfectJSON is a single-page application built with React and Vite. The tokenizer, linter, lossless number parser, formatter and diff engine are all custom, dependency-free implementations, so the production bundle stays small and loads quickly. Your documents and settings live in your browser's local storage, never on a server.
Browser compatibility
PerfectJSON runs in the current versions of the major browsers, on desktop and mobile:
- Google Chrome
- Mozilla Firefox
- Apple Safari
- Microsoft Edge
JavaScript needs to be enabled, since all processing happens locally in the browser.
Privacy Policy
Last updated: July 14, 2026
This privacy policy explains what information PerfectJSON (“we”, “us”), available at perfectjson.com, collects and how it is used. In short: the JSON documents you edit stay on your device, and the only data we handle is the standard, anonymous usage data described below.
The JSON you edit
The content you paste, type, open or generate in the editor is processed entirely in your browser. It is never transmitted to us or to any third party. Your documents and preferences are saved only in your browser's local storage on your own device, and you can clear them at any time from the app or your browser settings.
Analytics
We use Google Analytics to understand aggregate usage, such as which pages are visited and roughly how many people use the tool. Google Analytics sets cookies and collects standard information like your browser type, referring page and an approximate, IP-derived location. This data is aggregated and is not used to identify you personally. See Google's privacy policy, and opt out with the Google Analytics opt-out add-on.
Advertising and cookies
- We use Google AdSense to display ads. Third-party vendors, including Google, use cookies to serve ads based on your prior visits to this and other websites.
- Google's use of advertising cookies enables it and its partners to serve ads to you based on your visit to this and/or other sites on the internet.
- You may opt out of personalized advertising by visiting Google Ads Settings, or opt out of a third-party vendor's use of cookies at aboutads.info.
- If you are in the European Economic Area, the United Kingdom or Switzerland, we show a consent message through a Google-certified Consent Management Platform, and ads are served according to the choice you make there.
What we do not do
We do not sell your personal information, we do not require an account, and we never receive the contents of your JSON documents.
Third-party links
Some pages link to external sites (for example the specifications and tools referenced in the guide). We are not responsible for the privacy practices or content of those sites.
Changes to this policy
We may update this policy from time to time. Material changes will be reflected here with a new “last updated” date. Questions? See Contact below.
Terms of Use
Last updated: July 14, 2026
By using PerfectJSON you agree to the following terms.
- Free service, provided “as is”. The tool is provided free of charge, without warranties of any kind, express or implied, including fitness for a particular purpose. We do not guarantee it will be uninterrupted, error-free, or that any operation (validation, auto-fix, conversion) is correct for every input.
- Your data is your responsibility. Because everything runs in your browser, you are responsible for keeping your own copies of anything important. We are not liable for any loss of, or changes to, your data.
- Limitation of liability. To the maximum extent permitted by law, we are not liable for any direct, indirect, incidental or consequential damages arising from your use of, or inability to use, the tool.
- Acceptable use. Do not attempt to disrupt the service, abuse it in a way that harms other users, or use it for any unlawful purpose.
- Changes. We may update the tool and these terms at any time. Continued use after changes constitutes acceptance of the updated terms.
Frequently asked questions
Does PerfectJSON upload my JSON?
No. Your JSON is processed entirely in your browser and is never sent to our servers. There is no upload step and no backend that could receive it.
Is PerfectJSON free?
Yes. There are no accounts, usage limits or paid plans. The tool is supported by unobtrusive display ads, which never see the JSON you edit.
Can I use PerfectJSON for API responses?
Yes. It can format, validate, compare and inspect JSON payloads, including large API responses. Because everything runs locally, it is safe even when the response contains tokens or personal data.
Does PerfectJSON store my JSON files?
No. Your documents stay on your device and are only kept in your browser's local storage if you choose to keep them.
Which browsers does PerfectJSON support?
Current versions of Chrome, Firefox, Safari and Edge, on desktop and mobile, with JavaScript enabled.
Can it handle very large numbers and 64-bit IDs?
Yes. Its lossless parser preserves integers above 253 − 1, so big database IDs survive formatting and editing without precision loss.
Contact
Spotted a bug, want a feature, or have a question about privacy or these terms? We'd like to hear from you.
- Feedback, bugs & feature requests: [email protected]
- Security & privacy: [email protected]
The changelog lists every release, and much of what PerfectJSON does exists because someone asked for it.