JSON Formatter & Validator
Paste JSON to format, minify and validate it — with exact line/column error locations, a collapsible tree view, key sorting and one-click copy or download.
Type or paste any JSON (or open a .json file) and the page validates it as you type. When it is
valid you can pretty-print it with your choice of indentation, minify it back to a single line, sort object
keys, explore it as an interactive collapsible tree, and copy or download the result. When it is invalid you
get the exact line and column, a caret pointing at the problem character, and a plain-English explanation for
the usual suspects — trailing commas, single quotes, comments, NaN and friends.
Your JSON
Tip: press Ctrl+Enter (or ⌘+Enter) inside the box to format.
Why JSON fails validation — the usual suspects
Strict JSON (defined in RFC 8259) is unforgiving. Almost every “my JSON is broken” report is one of these:
| Mistake | Example | Why it fails |
|---|---|---|
| Trailing comma | {"a": 1,} | Strict JSON forbids a comma before ] or } (unlike JavaScript object literals). |
| Single quotes | {"a": 'b'} | Strings — and keys — must use double quotes. |
| Comments | {"a": 1} // done | JSON has no comment syntax. // and /* */ belong to JSONC / JSON5. |
| Unquoted keys | {a: 1} | Every object key must be a double-quoted string. |
NaN / Infinity / undefined | {"a": NaN} | None of these can be represented in JSON — use null (or a number) instead. |
| Duplicate keys | {"a": 1, "a": 2} | Technically allowed, but most parsers silently keep the last value — usually a bug. This tool flags it as a warning. |
| Byte Order Mark | {"a": 1} | An invisible character some editors write at the start of a file. Save as UTF-8 without BOM. |
| Multi-line strings | a real newline inside "…" | A string cannot contain a raw newline — escape it as \n. |
Strict JSON vs JSON5 / JSONC
If your data “almost” parses, it is probably a JSON dialect. JSON5 (standardised in 2023)
relaxes the grammar: comments, single quotes, trailing commas, unquoted keys, NaN/Infinity
and hex numbers. JSONC is plain JSON plus comments — the format VS Code uses for its
settings.json. This tool validates strict JSON only, and the error messages will tell you when a
mistake looks like one of those dialects.
How the error location works
Line and column are 1-based, with the column counted from the start of the line (the same convention as
most editors). The snippet under the error shows a few lines of context with a ^ caret under
the offending character. The parser on this page is written in plain JavaScript — rather than relying
on JSON.parse, whose error messages vary by browser and usually only give a character offset
— so every error can point at the exact line and column with an actionable message.
Nothing on this page leaves your browser: there is no server round-trip when you paste, format or validate, no analytics on your inputs, and no storage of any kind.
