Locator work starts faster when Appium Inspector opens a real session instead of only saving a capability file. A failed launch usually means the server URL, remote path, driver, target device, or capability payload is wrong, so the first successful Inspector screen should show both the live app image and its source tree.
The Session Builder connects to a standalone Appium server from the Appium Server tab. A local server with default settings uses Remote Host 127.0.0.1, Remote Port 4723, Remote Path /, and SSL off; older Appium 1 servers may need /wd/hub, but Appium 2 and Appium 3 default to the server root.
The Capability Builder sends the same W3C capability object that a client library would use. Keep Appium extension keys prefixed with appium: in raw JSON, start with a known target such as Android Settings through UiAutomator2, and treat the Session Inspector screen as ready only when the screenshot panel, source tree, and selected-element attributes update.
$ curl --silent http://127.0.0.1:4723/status {"value":{"ready":true,"message":"The server is ready to accept new connections","build":{"version":"3.5.0"}}}
Start the server first if this request fails.
Related: How to start the Appium server
Use Remote Host 127.0.0.1, Remote Port 4723, Remote Path /, and leave SSL off for a default local server. Use /wd/hub only for an Appium 1 server started with that base path.

{
"platformName": "Android",
"appium:automationName": "UiAutomator2",
"appium:deviceName": "Android Emulator",
"appium:udid": "emulator-5554",
"appium:appPackage": "com.android.settings",
"appium:appActivity": ".Settings"
}
Replace emulator-5554 with the target serial. Use appium:app for an APK path, or switch to XCUITest and appium:bundleId for an iOS app.
Related: How to configure Appium capabilities
The target device, emulator, or simulator must be unlocked and reachable; otherwise the Inspector reports a session creation error from the Appium server or driver.
The screenshot panel and source tab prove that the Inspector has an active session, not just saved capabilities.

Prefer stable values such as resource-id, accessibility id, label, name, or text over screen coordinates when the app exposes them.
Ending the session releases the device for the next Inspector or client-library run.