rpc_estimate_smart_fee

THE RISK

Low Risk

Why rpc_estimate_smart_fee needs a policy

This tool queries the Bitcoin network to retrieve fee rate information for transaction planning. It has no side effects, does not move funds, does not execute transactions, and does not modify any data. It is purely informational and read-only, used by clients to determine appropriate transaction fees before broadcasting.

From the tool's definition Tool name 'rpc_estimate_smart_fee' and description 'Estimate approximate fee per kilobyte (kB) needed for a transaction' — retrieves fee estimation data without modifying state or executing transactions.

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

POLICY

How to control rpc_estimate_smart_fee

PolicyLayer is an MCP gateway — it sits between your AI agents and Maestro MCP Server, and nothing reaches the server without passing your rules. This is the rule we recommend for rpc_estimate_smart_fee:

policy.json

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

rpc_estimate_smart_fee 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 Maestro MCP Server — 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 rpc_estimate_smart_fee

What does the rpc_estimate_smart_fee tool do? +

Estimate approximate fee per kilobyte (kB) needed for a transaction. Useful for setting dynamic fee rates in wallets or broadcast tools. It is categorised as a Read tool in the Maestro MCP Server MCP Server, which means it retrieves data without modifying state.

How do I enforce a policy on rpc_estimate_smart_fee? +

Register the Maestro MCP Server MCP server in PolicyLayer and add a rule for rpc_estimate_smart_fee: 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 Maestro MCP Server. Nothing to install.

What risk level is rpc_estimate_smart_fee? +

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

Can I rate-limit rpc_estimate_smart_fee? +

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

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

rpc_estimate_smart_fee is provided by the Maestro MCP Server MCP server (maestro-org/maestro-mcp-server). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.

Enforce policy on every Maestro MCP Server tool call.

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

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