JSONLint - JSON Lint is a web based validator and reformatter for JSON, a lightweight data-interchange format.
JSONFormatter.org - Online JSON Formatter and JSON Validator will format JSON data, and helps to validate, convert JSON to XML, JSON to CSV. Save and Share JSON
JSON Formatter & Validator - The JSON Formatter was created to help with debugging.
JSON Editor Online - View, edit and format JSON online
Tool Slick JSON Formatter - Online tool to format, indent, syntax highlight & visualize JSON data.
BeautifyCode.net - This development tool gives you formatters, beautifiers, minifiers, validations, and converters for a technical person's daily task. You can convert xml to json, json and yaml, numbers to words and other data.