There are lots of good Internet speed tests, such as Waveform, Cloudflare, or Speedtest.net. Unfortunately, these mix your ISP's performance with your local router/network so it's hard to tease out whether problems are local or remote.

The Crusader network speed and latency test does a remarkably good job of measuring the performance of your local network – transfer rates and latency – both for Ethernet and Wi-Fi.

To use Crusader, you'll need two computers – one acting as a server, the other as a client. To run a test, download the pre-built binary onto two computers (it runs on Windows, macOS, or Linux). Connect the first computer to one of your router's LAN Ethernet ports, and start it as a Server. Connect the other computer via WiFi and start the Client, enter the server's address, and start the test.

Read about how to interpret the Crusader results or more about running local tests in the Crusader docs. NB: These documents are waiting to be incorporated into to the main Crusader repo.