Follow a library (by UUID) or a remote channel (by actor URL/handle @user@server). Rate-limited: 30/hour.
AI agents use fw_follow 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.
Following a library or remote channel creates a persistent subscription/relationship, which is a reversible write action (can be unfollowed). It modifies state by establishing a follow relationship but does not delete data or move money. Medium severity because it could be misused to follow unintended entities or expose the user's identity/network to remote servers.
From the tool's definition Follow a library (by UUID) or a remote channel (by actor URL/handle @user@server)
Documented attack patterns abuse exactly the kind of access fw_follow 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_follow:
{
"version": "1",
"default": "deny",
"tools": {
"fw_follow": {
"limits": [
{
"counter": "fw_follow_rate",
"window": "minute",
"max": 30,
"scope": "grant"
}
]
}
}
}fw_follow 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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Follow a library (by UUID) or a remote channel (by actor URL/handle @user@server). 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 fw_follow: 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_follow 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 fw_follow 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_follow. 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_follow 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.