Hold down a specific keyboard key until released.
AI agents invoke key_down to trigger actions in Computer Control MCP. What it does depends on the arguments the agent supplies, and its effects often reach beyond the immediate call — builds kicked off, notifications sent, workflows started.
This tool simulates holding a keyboard key on the user's computer. It can be used to trigger arbitrary keyboard shortcuts, modifier key combinations (e.g., holding Ctrl, Alt, Shift, Win/Cmd), or continuous input, enabling broad system-level actions such as opening system dialogs, triggering shortcuts that delete or modify data, or combined with other tools to perform complex automated actions.
From the tool's definition Hold down a specific keyboard key until released
Documented attack patterns abuse exactly the kind of access key_down gives an agent:
PolicyLayer is an MCP gateway — it sits between your AI agents and Computer Control MCP, and nothing reaches the server without passing your rules. This is the rule we recommend for key_down:
{
"version": "1",
"default": "deny",
"tools": {
"key_down": {
"limits": [
{
"counter": "key_down_rate",
"window": "minute",
"max": 10,
"scope": "grant"
}
]
}
}
}key_down stays usable, but rate-capped — a runaway agent can't fire it dozens of times a minute. Everything else on the server is denied unless you say otherwise.
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Hold down a specific keyboard key until released. It is categorised as a Execute tool in the Computer Control MCP MCP Server, which means it can trigger actions or run processes. Use rate limits and argument validation.
Register the Computer Control MCP server in PolicyLayer and add a rule for key_down: allow, deny, rate-limit, or require approval. Point your MCP client at the PolicyLayer proxy URL and the rule is enforced on every call, before it reaches Computer Control MCP. Nothing to install.
key_down is a Execute tool with high risk. Execute tools should be rate-limited and have argument validation enabled.
Yes. Add a rate_limit block to the key_down rule in your PolicyLayer policy. For example, setting max: 10 and window: 60 limits the tool to 10 calls per minute. Rate limits are tracked per agent session and reset automatically.
Set action: deny in the PolicyLayer policy for key_down. The AI agent will receive a policy violation error and cannot call the tool. You can also include a reason field to explain why the tool is blocked.
key_down is provided by the Computer Control MCP server (ab498/computer-control-mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
Deterministic rules across all 15 Computer Control MCP tools. Per-identity grants. Full audit log. Live in minutes. Nothing to install.
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15 Computer Control MCP tools catalogued and risk-classified — across an index of 42,500+ MCP servers.