About FMTLY

A JSON workspace in your browser

FMTLY is a free online JSON formatter, validator, editor and comparison tool. Open a file or paste JSON, inspect its structure and download the result. No account is required.

Format and validate JSON

1. Paste JSON into the editor, choose Open file, or drop a file into the workspace. Each opened document gets its own tab.
2. Choose Format to make JSON easier to read. Use Minify when you need a compact result. Syntax errors are shown so you can correct them.
3. Switch between Code, Text, Tree, Form and View. Download a copy when you are ready to keep your changes.

Formatting preserves number tokens, string escapes, member order and duplicate keys. Sorting keys is a separate action. Form view keeps existing structure and value types; use Code or Tree when you need structural changes.

Compare two JSON documents

Open Compare, put the original JSON on the left and the modified JSON on the right, then run the comparison. Review added, removed and changed values, or export the changes. Object member order is ignored. Arrays can be matched by position or a unique identity field, and specific JSON Pointer paths can be ignored.

Comparison requires unique object keys and displays up to 1,000 changes. Comparison documents are not saved automatically.

Use JSON Schema and inspection tools

Attach a JSON Schema to a document to check its shape and get suggestions. FMTLY supports draft-07 schemas with local references. It reports incomplete validation when it encounters unsupported precision or other limitations, including schemas with a literal __proto__ property constraint. An incomplete result is not a successful validation.

Use the outline to find keys, a JSON Pointer to jump to a value, Search all documents to find content across tabs, or Table view to explore an array of objects and export CSV.

Local drafts and browser processing

Formatting, editing and validation run in your browser. Remember workspace is off by default. Turn it on to keep open documents, schemas and revision history on this device. Turning it off removes those saved drafts and revisions. Download important work independently; browser storage can be cleared.

The website offers optional analytics. Choose Essential only to keep Google Analytics and Microsoft Clarity disabled. Read about data and cookie choices.

Frequently asked questions

Is FMTLY free?

Yes. The editor is available without a subscription or account.

Does it work offline?

Once the editor has loaded, its core formatting, editing and comparison tools can continue without a network connection. Loading or reloading the website still requires a connection; this package does not install an offline cache.

How large can a document be?

The workspace supports up to 5 MiB per document, 100,000 values and 256 nesting levels. Practical performance also depends on your device and browser.

Which browser should I use?

Use a current browser with JavaScript enabled. Files, clipboard access and local storage may be restricted by your browser settings.

Open-source credits

The editor bundles Ace, Split.js, Fuzzysort and Ajv. It includes JetBrains Mono and IBM Plex fonts, and icons adapted from Microsoft Codicons. See the full license notices.