Cancel a running Proctor exam. Stops an exam that is currently executing on a Fly machine. This is useful when you need to abort a test that is taking too long or encountering issues. Returns: - Result object indicating the cancellation status Use cases: - Stop a stuck or slow exam - Cancel a tes...
AI agents invoke cancel_exam to trigger actions in Playwright Stealth. 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 triggers an external operation — terminating/cancelling a running process on a remote Fly machine. It is an Execute-category action because it sends a command to stop an active external process. It is not Destructive (no data is irreversibly deleted), but it does affect running infrastructure.
From the tool's definition Stops an exam that is currently executing on a Fly machine... abort a test that is taking too long... Cancel a test started with wrong parameters... Free up resources for other tests... Gracefully terminate a running exam
Documented attack patterns abuse exactly the kind of access cancel_exam gives an agent:
PolicyLayer is an MCP gateway — it sits between your AI agents and Playwright Stealth, and nothing reaches the server without passing your rules. This is the rule we recommend for cancel_exam:
{
"version": "1",
"default": "deny",
"tools": {
"cancel_exam": {
"limits": [
{
"counter": "cancel_exam_rate",
"window": "minute",
"max": 10,
"scope": "grant"
}
]
}
}
}cancel_exam 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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Cancel a running Proctor exam. Stops an exam that is currently executing on a Fly machine. This is useful when you need to abort a test that is taking too long or encountering issues. Returns: - Result object indicating the cancellation status Use cases: - Stop a stuck or slow exam - Cancel a test started with wrong parameters - Free up resources for other tests - Gracefully terminate a running exam before destroying the machine Note: - The exam must be currently running on the specified machine - After cancellation, the machine may still need to be destroyed separately - Results from a cancelled exam will not be saved automatically. It is categorised as a Execute tool in the Playwright Stealth MCP Server, which means it can trigger actions or run processes. Use rate limits and argument validation.
Register the Playwright Stealth MCP server in PolicyLayer and add a rule for cancel_exam: 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 Playwright Stealth. Nothing to install.
cancel_exam 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 cancel_exam 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 cancel_exam. 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.
cancel_exam is provided by the Playwright Stealth MCP server (pulsemcp/mcp-servers). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
Start from Playwright Stealth, add the rest of your stack, and see everything your agents can call. Then put policy on all of it.
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68 Playwright Stealth tools catalogued and risk-classified — across an index of 43,000+ MCP servers.