Subscribe to a channel by handle (name@host). Rate-limited: 30/hour.
AI agents use pt_subscribe to create or update resources in Crow — usually the action step of a workflow, after the agent has gathered context. Every call changes real data in your Crow environment.
Subscribing to a channel is a write operation that creates a persistent subscription record. It is reversible (can unsubscribe), so it doesn't qualify as Destructive. It involves no code execution or financial transaction. Severity is medium because misuse could spam subscriptions or create unwanted federation relationships across platforms, though the rate limit (30/hour) constrains blast radius.
From the tool's definition 'Subscribe to a channel by handle (name@host)' — subscribing creates a new subscription relationship/record
Documented attack patterns abuse exactly the kind of access pt_subscribe 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 pt_subscribe:
{
"version": "1",
"default": "deny",
"tools": {
"pt_subscribe": {
"limits": [
{
"counter": "pt_subscribe_rate",
"window": "minute",
"max": 30,
"scope": "grant"
}
]
}
}
}pt_subscribe stays usable, but capped — an agent stuck in a loop can't make hundreds of changes a minute. Everything else on the server is denied unless you say otherwise.
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Subscribe to a channel by handle (name@host). Rate-limited: 30/hour. It is categorised as a Write tool in the Crow MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.
Register the Crow MCP server in PolicyLayer and add a rule for pt_subscribe: 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.
pt_subscribe is a Write tool with medium risk. Write tools should be rate-limited to prevent accidental bulk modifications.
Yes. Add a rate_limit block to the pt_subscribe 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 pt_subscribe. 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.
pt_subscribe 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.
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576 Crow tools catalogued and risk-classified — across an index of 43,000+ MCP servers.