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+API = Application Programming Interface. This is the way other
+applications can communicate with Piwigo. This feature is also know as
+*Web Services*.
+
+Examples:
+
+-   Wordpress (web blog software) can display random photos from a
+    Piwigo gallery in its sidebar
+-   Lightroom (photo management software for desktop) can create albums
+    and upload photos to Piwigo
+
+This documentation is under construction: not all methods are described
+here. You won't have to find methods by yourself in Piwigo source code,
+we have a web API browser, distributed in Piwigo itself. On any Piwigo
+installation, go to <http://yourdomain/yourpiwigo/tools/ws.htm> from
+your web browser and discover all methods. For example [web API browser
+on Piwigo demo](https://demo1.piwigo.com/tools/ws.htm).
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