pf_follow

THE RISK

Medium Risk

Why pf_follow needs a policy

Following an account creates a social relationship/connection on the platform, which is a reversible write action (can be unfollowed). It modifies state by establishing a follow relationship. Not destructive since it can be undone, and not financial or execute-category.

From the tool's definition Follow an account by handle (@user@domain) or local account ID

Documented attack patterns abuse exactly the kind of access pf_follow gives an agent:

POLICY

How to control pf_follow

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 pf_follow:

policy.json

{
  "version": "1",
  "default": "deny",
  "tools": {
    "pf_follow": {
      "limits": [
        {
          "counter": "pf_follow_rate",
          "window": "minute",
          "max": 30,
          "scope": "grant"
        }
      ]
    }
  }
}

pf_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.

Create a free account and register Crow — nothing to install.
Add this policy — paste it, or build it visually.
Point your MCP client (Claude, Cursor, anything) at your gateway URL.

LIMIT THIS TOOL →

Free to start. No card required.

EXPLORE

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Write tools on other servers

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Go deeper

The MCP Attack Database → Documented attack patterns against MCP deployments — and the policies that stop them.
Argument validation → Checking tool call arguments against schema and policy before they run.
Scoped token → Per-person credentials that grant a defined subset of servers and tools.
Rate Limiting MCP Tool Calls: A Practical Guide →
MCP Security: Why Prompt Guardrails Aren't Enough →

FAQ

Questions about pf_follow

What does the pf_follow tool do? +

Follow an account by handle (@user@domain) or local account ID. 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.

How do I enforce a policy on pf_follow? +

Register the Crow MCP server in PolicyLayer and add a rule for pf_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.

What risk level is pf_follow? +

pf_follow is a Write tool with medium risk. Write tools should be rate-limited to prevent accidental bulk modifications.

Can I rate-limit pf_follow? +

Yes. Add a rate_limit block to the pf_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.

How do I block pf_follow completely? +

Set action: deny in the PolicyLayer policy for pf_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.

What MCP server provides pf_follow? +

pf_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.

Enforce policy on every Crow tool call.

Start from Crow, add the rest of your stack, and see everything your agents can call. Then put policy on all of it.

CHECK YOUR STACK →