Stop the currently-playing audio stream on the paired glasses and clear any queued tracks. This is a hard stop with no resume. For temporary pause, use fw_pause instead.
AI agents invoke fw_stop_playback to trigger actions in Crow. 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 on a device (paired glasses) whose effects depend on execution context and timing. While not destructive to data (does not delete/overwrite persistent information), it executes a command that halts a currently-running process with immediate external consequences.
From the tool's definition Tool performs a hard stop action on paired glasses audio playback with irreversible effect ('hard stop with no resume'). Clears queued tracks without user confirmation.
Documented attack patterns abuse exactly the kind of access fw_stop_playback gives an agent:
PolicyLayer is an MCP gateway — it sits between your AI agents and Crow, and nothing reaches the server without passing your rules. This is the rule we recommend for fw_stop_playback:
{
"version": "1",
"default": "deny",
"tools": {
"fw_stop_playback": {
"limits": [
{
"counter": "fw_stop_playback_rate",
"window": "minute",
"max": 10,
"scope": "grant"
}
]
}
}
}fw_stop_playback 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.
Free to start. No card required.
Stop the currently-playing audio stream on the paired glasses and clear any queued tracks. This is a hard stop with no resume. For temporary pause, use fw_pause instead. It is categorised as a Execute tool in the Crow MCP Server, which means it can trigger actions or run processes. Use rate limits and argument validation.
Register the Crow MCP server in PolicyLayer and add a rule for fw_stop_playback: 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 Crow. Nothing to install.
fw_stop_playback 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 fw_stop_playback 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 fw_stop_playback. 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.
fw_stop_playback is provided by the Crow MCP server (kh0pper/crow). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
Start from Crow, add the rest of your stack, and see everything your agents can call. Then put policy on all of it.
Free to start. No card required.
576 Crow tools catalogued and risk-classified — across an index of 43,000+ MCP servers.