s4_echo_plain

THE RISK

Low Risk

Why s4_echo_plain needs a policy

This tool takes a string input and returns it unchanged. It performs no side effects, makes no modifications to data, executes no code, and triggers no external operations. It is a pure read/echo operation that retrieves and returns the input provided. Even though the description is minimal, the function is clearly informational only.

From the tool's definition Tool name and description: 's4_echo_plain' described as 'Echo a code back. Call with any string code.' - a simple echo/reflection operation with no data modification, deletion, or external execution.

Documented attack patterns abuse exactly the kind of access s4_echo_plain gives an agent:

POLICY

How to control s4_echo_plain

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 s4_echo_plain:

policy.json

{
  "version": "1",
  "default": "deny",
  "tools": {
    "s4_echo_plain": {}
  }
}

s4_echo_plain is read-only, so it stays allowed — but 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.

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EXPLORE

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FAQ

Questions about s4_echo_plain

What does the s4_echo_plain tool do? +

Echo a code back. Call with any string code. It is categorised as a Read tool in the Crow MCP Server, which means it retrieves data without modifying state.

How do I enforce a policy on s4_echo_plain? +

Register the Crow MCP server in PolicyLayer and add a rule for s4_echo_plain: 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 s4_echo_plain? +

s4_echo_plain is a Read tool with low risk. Read-only tools are generally safe to allow by default.

Can I rate-limit s4_echo_plain? +

Yes. Add a rate_limit block to the s4_echo_plain 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 s4_echo_plain completely? +

Set action: deny in the PolicyLayer policy for s4_echo_plain. 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 s4_echo_plain? +

s4_echo_plain 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.

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