Port 3233: Whisker — The Neuroscience Experiment Controller

What Runs on Port 3233

Port 3233 is the main communication port for Whisker, a client-server behavioral research control system developed at the University of Cambridge. It is registered with IANA under the name "WhiskerControl main port" for both TCP and UDP, assigned in February 2002.¹

Whisker is not a general-purpose protocol. It lives in a specific world: the experimental psychology and behavioral neuroscience laboratory. It controls the hardware that runs animal experiments — digital input/output devices, touchscreens, keyboards, mice, sound cards, and reward dispensers. Researchers write client programs that connect to the Whisker server on port 3233 and issue commands to run behavioral tasks.

How Whisker Works

The protocol is deliberately simple. Whisker implements a plain-text, TCP-based command language. Any program that can open a network socket can be a Whisker client — the server doesn't care whether it's Python, C++, Java, or anything else.

The architecture separates concerns cleanly:

• The Whisker server runs on a dedicated machine, controls the physical hardware, and listens on port 3233
• Client programs connect over the network and issue commands ("open line 4," "play sound file X," "wait for input on line 2")
• The server executes those commands against real hardware and sends back events

This means a researcher can write a behavioral task in whatever language they prefer and run it on a different machine than the one controlling the hardware. The network becomes the experiment's nervous system.

The Story Behind It

Whisker was written by Rudolf Cardinal, then at the Department of Experimental Psychology at Cambridge, for use by the Behavioural and Cognitive Neuroscience Group. It was designed to replace older, less flexible hardware control systems and to make behavioral experiments easier to program, replicate, and share.²

The experiments it runs are serious science. Whisker has been used to study:

• Addiction and impulse control — rats choosing between immediate small rewards and delayed larger ones
• Cognitive flexibility — animals learning and unlearning rules
• Decision-making under uncertainty — probabilistic reward tasks in rodents, primates, and humans
• Attention and executive function — touchscreen tasks measuring sustained attention

The subjects have included rodents, nonhuman primates, dogs, pigs, and birds. The client software running over port 3233 has influenced what we know about the neurobiology of addiction and how the prefrontal cortex governs choice.

Campden Instruments Ltd holds a license to distribute Whisker commercially, and it underlies some of the most widely used behavioral task suites in neuroscience today.³

What This Port Looks Like in the Wild

You will not encounter port 3233 on the open Internet. Whisker runs in closed laboratory networks — the server machine is typically air-gapped or firewalled, connected only to the behavioral testing equipment and the researcher's workstation.

If you see port 3233 open on a machine outside a research context, it is worth investigating. It is not a common attack target, but any unexpected open port deserves scrutiny.

How to Check What's Listening

To see if something is listening on port 3233 on your machine:

macOS / Linux:

# Show what process is listening on port 3233
lsof -i :3233

# Or with ss (Linux)
ss -tlnp | grep 3233

Windows:

netstat -ano | findstr :3233

If you see a process listening on this port and you're not running a Whisker behavioral research server, check what it is. It could be a legitimate application that chose this port informally, or something that warrants a closer look.

Why This Port Exists in the Registry

Registered ports (1024-49151) exist so that applications can claim a port number without conflicting with every other application that needed one. IANA maintains the registry to prevent collisions — without it, two unrelated applications might both try to use the same port and step on each other.

Whisker registered port 3233 so that Whisker servers and clients across different institutions could use the same default port reliably. In practice, the registration mostly matters for documentation and convention. A Whisker server can be configured to use any port. But 3233 is the default, and that default being stable matters when you're trying to replicate an experiment from another lab.