JSON Formatter & Validator

Format, indent, and validate JSON entirely in your browser.

Paste JSON on the left to see it formatted on the right. Invalid JSON shows the exact parser error and byte offset inline so you can jump straight to the broken character.

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Input

Formatted output

{
  "hello": "world",
  "items": [
    1,
    2,
    3
  ]
}

About this tool

Uses the browser's built-in JSON.parse and JSON.stringify, which implement RFC 8259 strictly — no JSON5 extensions, no trailing commas, no comments, no unquoted keys. The 2-space / 4-space indent toggle controls JSON.stringify's third argument. Both panes are textareas you can copy out of with the standard browser shortcut. Nothing is uploaded — your input stays on your device.

When to use this

Reformatting compact API response bodies (one-line JSON) into something readable.
Validating syntax of a config file before committing it to a repo where invalid JSON would break the build.
Comparing two JSON snippets — paste one, copy the formatted output, paste the other, compare.
Quick sanity-checking JSON pasted from a logs / errors panel where strings have been escape-encoded.

Frequently asked questions

Does my JSON leave my browser when I paste it here?: No. The formatter runs entirely on your device using the browser's native JSON.parse / JSON.stringify. Nothing is sent to a server, nothing is logged, nothing is stored. You can verify by opening the Network tab in DevTools while you paste — you'll see no outbound requests on input change.
How is this different from JSONLint or jsonformatter.org?: Functionally, the parsing is identical because every JSON formatter on the web ultimately calls the same JSON.parse. The differences are UX: this tool is single-page, has no ads-on-input, has no upload-to-server step, supports 2- and 4-space indent toggle inline, and surfaces the parser error message at the exact byte offset when input is invalid.
Why does my JSON throw an error when it looks fine?: Common culprits: trailing commas (legal in JavaScript, illegal in JSON), single quotes around strings (must be double quotes), unquoted keys, comments (JSON doesn't support // or /* */), or unescaped control characters in strings. The error message in the right panel tells you the byte offset where parsing stopped — start checking just before that position.
Can it format JSON5 or JSONC (with comments)?: Not currently. The browser's native JSON.parse strictly rejects comments and trailing commas per RFC 8259. If you need to clean up JSONC for tooling that doesn't accept it, the workaround is to remove comments + trailing commas first (e.g. with a small editor macro) and then paste the result here.
Will this work on very large files (1MB+)?: Yes, up to roughly the limit of what your browser can hold in a textarea — typically tens of megabytes of JSON before scroll performance starts to degrade. JSON.parse itself is fast; the slow part is rendering the formatted output for very deep nesting. For genuinely huge JSON dumps (100MB+), use a streaming parser at the command line (jq, jc) instead of any browser tool.

Related tools

All processing happens entirely in your browser — no input is sent to our servers. Page reviewed and maintained by the infoz editorial desk; report bugs or request features via /contact.

About this tool

When to use this

Reformatting compact API response bodies (one-line JSON) into something readable.

Validating syntax of a config file before committing it to a repo where invalid JSON would break the build.

Comparing two JSON snippets — paste one, copy the formatted output, paste the other, compare.

Quick sanity-checking JSON pasted from a logs / errors panel where strings have been escape-encoded.

Frequently asked questions

Does my JSON leave my browser when I paste it here?

No. The formatter runs entirely on your device using the browser's native JSON.parse / JSON.stringify. Nothing is sent to a server, nothing is logged, nothing is stored. You can verify by opening the Network tab in DevTools while you paste — you'll see no outbound requests on input change.

How is this different from JSONLint or jsonformatter.org?

Functionally, the parsing is identical because every JSON formatter on the web ultimately calls the same JSON.parse. The differences are UX: this tool is single-page, has no ads-on-input, has no upload-to-server step, supports 2- and 4-space indent toggle inline, and surfaces the parser error message at the exact byte offset when input is invalid.

Why does my JSON throw an error when it looks fine?

Common culprits: trailing commas (legal in JavaScript, illegal in JSON), single quotes around strings (must be double quotes), unquoted keys, comments (JSON doesn't support // or /* */), or unescaped control characters in strings. The error message in the right panel tells you the byte offset where parsing stopped — start checking just before that position.

Can it format JSON5 or JSONC (with comments)?

Not currently. The browser's native JSON.parse strictly rejects comments and trailing commas per RFC 8259. If you need to clean up JSONC for tooling that doesn't accept it, the workaround is to remove comments + trailing commas first (e.g. with a small editor macro) and then paste the result here.

Will this work on very large files (1MB+)?

Yes, up to roughly the limit of what your browser can hold in a textarea — typically tens of megabytes of JSON before scroll performance starts to degrade. JSON.parse itself is fast; the slow part is rendering the formatted output for very deep nesting. For genuinely huge JSON dumps (100MB+), use a streaming parser at the command line (jq, jc) instead of any browser tool.