How to access localhost from android over wifi

First of all you need to host your web site or your web service in your machine web server. Hope you know it already.

Your Web server(system in which you host your site) and your mobile should be in same network connection.

1. Open your Control Panel and select System and Security.
2. Select Windows Firewall and from that select Advanced settings from the left panel.
3. From the Advanced settings, on the left side Right Click Inbound Rules and select New Rule.
4. From the pop up open select Port and click Next.
5. Specific the local port(The ports should be same as that of the port  which you specified in your site ip in web server).
6. Give some name to your rule and click Finish.

Now connect your mobile to network through wifi. You can view your hosted site by searching your web ip  (specified for your web site in web server).