Take action on a Scrapybara instance through an agent. The agent can control the instance with mouse/keyboard and bash commands.
AI agents invoke act to trigger actions in Scrapybara 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 permits execution of arbitrary code and system commands on a virtual Ubuntu desktop through an agent interface. While it does not permanently delete data (which would be Destructive), it can trigger external operations, modify system state, install software, exfiltrate data, and perform any action a bash shell permits.
From the tool's definition Tool description states it 'can control the instance with mouse/keyboard and bash commands.' Server description indicates the tool enables clients to 'run code' and 'control instances through mouse/keyboard actions and bash commands.' The 'act' tool directly…
Documented attack patterns abuse exactly the kind of access act gives an agent:
PolicyLayer is an MCP gateway — it sits between your AI agents and Scrapybara MCP, and nothing reaches the server without passing your rules. This is the rule we recommend for act:
{
"version": "1",
"default": "deny",
"tools": {
"act": {
"limits": [
{
"counter": "act_rate",
"window": "minute",
"max": 10,
"scope": "grant"
}
]
}
}
}act 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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Take action on a Scrapybara instance through an agent. The agent can control the instance with mouse/keyboard and bash commands. It is categorised as a Execute tool in the Scrapybara MCP MCP Server, which means it can trigger actions or run processes. Use rate limits and argument validation.
Register the Scrapybara MCP server in PolicyLayer and add a rule for act: 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 Scrapybara MCP. Nothing to install.
act 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 act 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 act. 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.
act is provided by the Scrapybara MCP server (scrapybara/scrapybara-mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
Start from Scrapybara MCP, add the rest of your stack, and see everything your agents can call. Then put policy on all of it.
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5 Scrapybara MCP tools catalogued and risk-classified — across an index of 43,000+ MCP servers.