JSONLint - JSON Lint is a web based validator and reformatter for JSON, a lightweight data-interchange format.
Altova XMLSpy - The XMLSpy XML Editor is a powerful tool for editing XML and related technologies. It is the only XML Editor with patented SmartFix validation, enterprise-grade editors, converters, debuggers, and code generators.
JSON Buddy - JSON editor and validator - view, edit and format JSON data
Oxygen XML Editor - Oxygen XML Editor provides a comprehensive suite of XML authoring and development tools.
JSON Viewer - The most beautiful and customizable JSON/JSONP highlighter that your eyes have ever seen.
Liquid Studio - XML Tools Provider: XML Studio - Graphical XML Schema Editor.