Stanislav Khromov

This plugin provides JSON and XML output formats for Toolset Views.
The plugin will also fetch all available custom fields for each post, making it truly simple to integrate WordPress 
with other systems that speak JSON and XML.
New in version 2.0
This plugin now supports Taxonomy and User queries!
Usage
Basic usage
Create your View, go to Settings -> Views Output Formats and pick your format. You will get a link to the XML or JSON version of the query.
<h3>Requirements</h3>
<ul>
<li>PHP 5.3 or higher</li>
</ul>
<h3>Translations</h3>
<ul>
<li>None</li>
</ul>
<h3>Upcoming features</h3>
Support for attaching taxonomy data to posts is planned
Feel free to contribute over at GitHub: 
https://github.com/khromov/wp-views-output-formats

Views Output Formats

Export your WordPress data in XML and JSON formats easily!

Tom Auger

This plugin, once activated, spits out the information passed by each filter used in manipulating database queries, as a learning tool.
The code itself is heavily documented and demonstrates best practices for working with those filters and actions to view / manipulate the query.
It is very important to note that this plugin is not meant for a production environment as it will insert a lot of really ugly HTML throughout your page. You’ll get the most use out of this plugin by looking at its code, and maybe previewing one or two pages on a sandbox, vanilla WordPress site.

Valz Display Query Filters

This demonstration plugin identifies the primary filters that are used by WordPress as it parses your queries.

Views Output Formats vs Valz Display Query Filters