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MCS Spy - display Wi-Fi MCS index usage in real-time

MCS is 'Modulation and Coding Scheme' and directly indicates which Mbps PHY speed is being used in Wi-Fi (tables).

MCS Spy: There is no such thing as a single PHY speed used by a Wi-Fi client. There is a Tx PHY speed and a Rx PHY speed, and these two speeds can actually jump around a lot every single second. MCS Spy was written to spy upon the actual MCS indexes used by a router/AP -- in real-time!
TIP: To spy on the MCS indexes used by a Wi-Fi client device (tablet, smartphone, PC, etc), disconnect all other wireless devices from the router/AP band being used, except for the ONE device you want to analyze. Then connect the MCS Spy PC to the router via Ethernet (or the other wireless band), and analyze.
Routers/AP supported: Any (Linux) router/AP that has a Qualcomm Atheros based Wi-Fi chipset that you can 'telnet' to should work. Google your router model plus 'wiki wifi chipset' and one of the top hits should tell you if your router/AP uses a Qualcomm chipset.
MCS Spy was developed and tested against a Netgear R7800 router. The R7800's /debug.htm web page allows Telnet to be enabled on the router.
Requirements: Must have a Java VM installed (see for help) in order to run the "mcsspy.jar" Java executable file contained within the download ZIP. The router being monitored must support 'telnet' (see prior paragraph on supported routers).

Download/Extract: Download, extract all files contained within this ZIP into a temp folder (eg: C:\mcsspy), and get started by reviewing the "readme.txt" file.

Run: Type "java -jar mcsspy.jar" to run MCS Spy, and get command line usage information displayed. In short, you just need to run MCS Spy and provide it with your router's ip address and telnet password.

MCS indexes: For help with MCS indexes (and PHY speeds), review this very helpful resource.

Donate: If you find MCS Spy helpful, support it by using PayPal's 'send money' feature -- send a donation to
This document is Copyright © 2020 Jerry Jongerius