Is here any way to let me develop a plugin in Ghost?

I want to build a plugin to make people easier test their mailgun configration.

but i don’t know how to start
(have wordpress plugin & theme development experience)

Ghost doesn’t really have a plugin ecosystem that’s comparable to Wordpress. You can build integrations, but these will mainly use webhooks or the normal Ghost API to communicate with Ghost.

Here is an overview of integrations that are available: Ghost integrations – official apps, plugins & tools

I’d start by having a look at these and how they integrate. Based on that, you should then be able to figure out if and how you’re integration can be created.

got it. i will check ghost integrations.