AI agents invoke key_up 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.
key_up releases a keyboard key, which is a direct input action on the computer. It can be used to complete keystrokes that started with key_down, potentially executing commands, triggering shortcuts, or interacting with active applications. While a single key release alone is low-risk, in combination with other tools it enables arbitrary keyboard-driven execution.
From the tool's definition Release a specific keyboard key
Documented attack patterns abuse exactly the kind of access key_up 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_up:
{
"version": "1",
"default": "deny",
"tools": {
"key_up": {
"limits": [
{
"counter": "key_up_rate",
"window": "minute",
"max": 10,
"scope": "grant"
}
]
}
}
}key_up 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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Release a specific keyboard key. 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_up: 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_up 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_up 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_up. 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_up 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.