There's a generic ping plugin ( admin > app settings > plugin install > add new )

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I installed the Generic ping plugin. Thank you for the tip.

One thing I noticed, however, is that you can only use one "Ping service URL". That is crazy! I have several services that I want to ping.

Is there a way to add multiple URLs to ping?

No, you have to install the plugin each time you want to add a new ping service.