pin13
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pin13 is a collection of tools that aid in IndieWeb-friendly web development, including microformats parsing, character counting, JSON prettifying, and number converting.
It is operated by 
Aaron Parecki as a personal scratch domain, but is used by many developers in the IndieWeb community to help debug issues when working on their own sites.
The name "pin13" is a reference to the Arduino microcontroller boards, which are hard-wired with an LED on pin 13 that can be controlled from software to allow debugging without any external components.