JSON validation, formatting, and JSON Lines

JSON is simple enough to write by hand and unforgiving enough that a single trailing comma breaks an entire pipeline. The tools on this site split the problem into distinct jobs: validate, format, transform, and choose the right on-disk shape.

Validation is not schema validation

A JSON validator checks syntax: brackets, quotes, commas, and value types. That is enough to answer "is this document parseable?" and to show the position of the first error. It does not check that your document matches an API contract. For that, you need a JSON Schema validator. Start with JSON validator to rule out syntax problems, then reach for schema tooling if the syntax is already valid.

One practical warning: JavaScript numbers cannot represent all large integers exactly. If you see a large ID lose digits, the fix is to quote it as a string at the source.

Formatting is safe

Pretty-printing only changes whitespace. Keys and values stay in order, which is why Format JSON can be used on configuration you intend to commit. Sorting keys is a separate, deliberate change, handled by Sort JSON keys.

Transformations work best as a pipeline

• Flatten JSON turns nested data into path records that are easy to diff, store, or review. The result is reversible.
• Unflatten JSON restores the nested structure from those records and reports conflicting paths instead of silently overwriting values.
• Merge JSON layers documents with an explicit conflict preview and a clear rule for arrays.
• Compare JSON reports structural differences, so reformatting does not create noise.
• JSON tree viewer explores large documents branch by branch and exports the exact value or JSON Pointer path you select.

When JSON Lines is the right shape

JSON Lines (also called NDJSON) stores one JSON value per line. It is the natural format for logs and streaming imports, because a reader can process a line at a time without loading the whole file. Pretty-printed JSON spanning multiple lines is not valid JSON Lines, and that mismatch is the most common cause of line errors reported by JSON Lines converter. The converter goes both directions and points to the exact failing line.

Practical limits

The JSON workspace accepts up to 1,000,000 characters, 50,000 values, and 64 levels of nesting. Live previews pause on very large inputs, and the run action still processes the full supported document.