Retrieve Context Key inside snippets. See https://forums.modx.com/thread/30357/solved-return-the-current-context-key for more details.

contextKey.snippet.php

<?php
/*
 * Usage [[!contextKey]]
 * */
 
return $modx->context->key;

getContext.snippet.php

<?php
/*
* Usage [[!getContext? &id=``]]
*/
 
//retrieve ID or use current resource
$id = (!empty($id) ? $id : $modx->resource->get('id'));
 
//retrieve context
$page = $modx->getObject('modResource', $id);
$output = $page->get('context_key');
 
//return output
return $output;