Make an HTTP GET request to your Appium server's /wd/hub/status endpoint. If the server is running, you should receive a JSON response with build details about the server.
Example response from my Appium server (listening at localhost:4723, GET request sent to localhost:4723/wd/hub/status):
{"status": 0,
"value": {
"build":
{
"version": "1.5.1",
"revision": "8150b4f3a64a9eb74d447552d3384aa192407eeb"
}
},
"sessionId": null
}