JSONP Viewer

Firebug, the Firefox add-on offers the best view among commonly used browser developer tools to visualize the JSON feed provided by an API.
reviewing JSON in Firebug

However, all native browser Developer Tools show JSONP data as a blob of plain text that is hard to make sense of. JSON with Padding or JSONP's purpose is to circumvent the same-source policy limitations of XMLHttpRequest.

JSON Viewer is a free tool that can present JSONP data in a tree view thereby enabling easy analysis. There is a small additional step though before you can view.
JSON Viewer - Text tab

After you paste JSONP into the textarea in the Text tab, click on the Strip to {} option in the toolbar

Now when you click on the Viewer tab, the JSONP will be better readable
JSON Viewer - Viewer tab

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