JSON Validator & Formatter

Format and validate a JSON document

Paste a JSON document into the editor and choose Format to check its syntax and apply the selected indentation. Minify performs the same parse check, then writes the document without unnecessary whitespace. Copy copies the current editor contents; Download saves them as a JSON file. Neither action independently validates the document, so format or minify it first.

Worked example: a trailing comma

The input {"items":[1,2,],"active":true} is invalid JSON because the array ends with a comma. Remove the comma to get {"items":[1,2],"active":true}, then choose Format. Select two or four spaces to change the indentation. Choose Minify to return to the compact representation. JSON requires double quotes around property names and strings; comments and JavaScript values such as undefined are not accepted.

What a successful check means

The tool uses the browser's JSON.parse function to check syntax and JSON.stringify to write the result. Passing this check means that the document is valid JSON, not that it matches an API contract. For example, {"quantity":"three"} parses successfully even if your application requires quantity to be a number. Required fields, allowed values, and application rules need a separate schema or application-level check.

Data preservation and size limits

Parsing converts JSON numbers to JavaScript numbers. Integers beyond Number.MAX_SAFE_INTEGER (9007199254740991) can lose precision. Keep long identifiers as quoted strings when you control the source format, and preserve the original file before reformatting. Duplicate object keys are also collapsed to the last value during parsing. Formatting is therefore not a byte-preserving transformation.

Parsing runs synchronously on the main browser thread, not in a streaming parser or background worker. Large or deeply nested documents can use substantial memory and temporarily freeze the page. There is no guaranteed 25 MB limit or performance benchmark. Use smaller samples for debugging and a suitable local file-processing tool for very large inputs.

Understanding errors

An invalid document leaves the editor contents in place and displays the browser's parse error message. Wording and position details differ between browsers. Inspect the reported location and the character before it: a missing comma or closing quote can cause the parser to complain at the next token. Tool inputs are processed in the browser; avoid pasting live credentials into web pages and use redacted samples when sharing a bug report.