What you need

Two PCs side by side in one room, each plugged into the same router or switch with a cable, on the same subnet, with a closed-back headset on each. Wi-Fi is not supported: it may still link, with more delay and gaps. Install from the Steam library on both PCs.

Everything the test needs, in one list. Please tick each one as it is ready.

• Two separate PCs, both physically hereExactly two: one host and one guest. A host that already has a guest shows as busy and turns a third PC away. One PC cannot be both host and joiner: each PC runs one copy. Sit at both; remote desktop, cloud PCs and VMs are not what it is made for (Q4, Q5).
• One subnet: the same router or switch, wiredBoth PCs wired by Ethernet (a USB Ethernet adapter works) to the same router or switch, on the same subnet of your own local network. Each PC shows its own address under This PC on the start screen; on most networks the first three numbers match, such as 192.168.1.160 and 192.168.1.21. Not a guest Wi-Fi, and not test machines kept apart by a DMZ, separate VLANs or isolation; if unsure, please ask your IT staff (Q6). Wi-Fi and play over the internet are not supported. The sound goes to the other PC and nowhere else: no accounts of its own, no telemetry, no analytics. It uses UDP ports 47800 and 47801; if a firewall is on, allow them on the local network (Q7).
• CO-OP Comms on the host PC, either app on the otherThe host PC runs CO-OP Comms (app 5409710). The joining PC runs CO-OP Comms or CO-OP Comms Client Only (app 5437680), a free download that only joins, never times out and never asks for payment. Both installed and started from the Steam library (Q1, Q2). The interface is in English.
• One microphone, plugged into the host PCOnly one microphone in the room: it plugs into the host PC, placed where it hears you, before the app opens. The joining PC needs no microphone (Q3).
• A closed-back headset on each PCOn both PCs, plugged in before the app opens: the host PC plays its own microphone in its own headset, and cannot host without one. Speakers would feed back into the microphone. A wired headset is best: a wireless one adds its own delay, though it works (Q3).
• Windows 11, 64-bit, on both PCsAt least a 64-bit dual-core processor, 4 GB of memory, Direct3D 12 and 50 MB of disk; a quad-core and 8 GB recommended. CO-OP Comms also runs on macOS 26 or later (Apple silicon) and on SteamOS 3 or a 64-bit Linux that runs Steam, with any two systems mixed or matched; this test uses two Windows PCs.

How the test is laid out

The test is 21 short steps in five stages: stage 1 on the host PC, stage 2 on the joining PC, stage 3 on both, then every control while linked (stage 4) and the start screen's extras (stage 5). Stages 1 to 3 are the main path; 4 and 5 try every other feature. Each step is one action, with a label such as 2C. If a step goes wrong, its Got stuck? page has the FAQ (Q1 to Q10) and what we know can go wrong there, each with its own label to quote back to us. Where these pages quote the app, the parts in angle brackets, such as host PC's address, are where your own name or address appears.

Words shaded like this stand for what your own screen shows there, such as your own user name or address.

In the pictures, "Tester 1" stands in for the host's Steam user name, "Tester 2" for the joining PC's, and "Tester 3" for a second host that is already busy. The addresses in them, 192.168.1.160 for the host PC and 192.168.1.21 for the joining PC, are examples; your windows show your own.