JSON Formatter & Validator

How it works

Validation is delegated to JSON.parse, the same strict parser used by every JavaScript engine, so a document that passes here is accepted by browsers, bundlers and runtime libraries alike. When the parser throws, this page reads the position out of the error message and turns it into a line and column in your own text. The message itself varies between engines, so the panel also inspects what is actually sitting at that position — a closing brace, a single quote, a curly quote, a bare word such as undefined — and adds a plain-language explanation plus a short excerpt with the character marked.

The three transformations are straightforward string operations once the value is parsed. Pretty-print re-serialises with JSON.stringify(value, null, indent) using the indent you chose — two spaces, four spaces or a tab. Minify re-serialises with no whitespace at all, which is what you want when pasting JSON into a query parameter, an environment variable or a compact storage key. Sort keys walks the whole structure — nested objects included, inside arrays too — and rebuilds every object with its keys in ascending string order, which makes two structurally identical payloads produce identical text and keeps version-control diffs readable.

The statistics are counted from the parsed value rather than from the text, so they describe the data instead of the formatting: the number of characters and lines on one side, and the count of top-level members plus the maximum nesting depth on the other. The tree view is generated on demand from the same parsed value. It is built entirely with DOM calls and text nodes, one collapsible <details> element per object or array, and it is capped at a few thousand nodes so that a multi-megabyte document cannot lock up the tab.

Accuracy, and where this tool stops

Everything here reflects a real parse, so there are no "looks valid" guesses: either JSON.parse accepted the text or it did not. Within that, four honest limits are worth knowing.

• Error positions are the engine's best effort. Chrome, Firefox and Safari word their SyntaxError messages differently, and some report only a line and column while others report a character offset. Where the engine gives no position at all, the excerpt falls back to the end of your input and says so rather than inventing a location. The character shown is where parsing stopped, which for a missing comma or an unfinished string can be a token or two past the real mistake.
• Formatting is not byte-for-byte preservation. Numbers are re-serialised by JavaScript, so 1.0 becomes 1, 1e2 becomes 100, and integers outside the safe range of ±2⁵³−1 can lose precision because they are held as IEEE-754 doubles. Leading zeros and other non-standard number spellings are rejected by the parser in the first place.
• Duplicate keys are silently collapsed. The specification says member names should be unique. If a document repeats one, JSON.parse keeps the last occurrence and the earlier ones disappear from the output. Nothing warns you, so a duplicate key is worth hunting for by hand in generated payloads.
• Sorting keys changes the text, not just the layout. The order of object members is not significant to JSON consumers, but it is significant to anything that hashes or signs the serialised bytes. Sort before you sign, not after, and expect diffs to move.

How to use it

1. Paste and watch the status line. Validation runs about a fifth of a second after you stop typing. A green result describes the shape of the document; a red one opens the error panel with the line, the column, the offending character and the excerpt.
2. Fix the first error, then look again. A parser stops at the first problem, so it reports one issue at a time. Repair the marked position, and the next error — if there is one — will be reported in the same way. Trailing commas are the most common cause and the easiest to spot.
3. Choose an indent, then pretty-print. Two spaces suit most APIs and codebases, four spaces match older style guides, and tabs let each reader set their own width. Changing the indent re-formats the current text immediately, so you can compare the three options.
4. Minify or sort when you need to. Minify removes every optional space and line break. Sort keys rebuilds each object alphabetically, recursively, which is the usual way to make two documents comparable with a plain text diff.
5. Inspect, then take the result away. Open the tree view to confirm the shape and drill into a nested value, then use Copy for the clipboard or Download as .json to save the current text as a file. Clear empties the box and the tree in one click.

The Load a sample button drops in a small document with nested objects and an array, which is a quick way to see what the error panel, the statistics and the tree view look like before you paste your own data.