estimate-fee-per-gas

THE RISK

Low Risk

Why estimate-fee-per-gas needs a policy

This is a query operation that reads blockchain data to inform transaction cost estimation. It does not execute transactions, modify state, delete data, or commit financial resources. The tool provides informational output to help users understand potential costs before they choose to proceed with a separate transaction operation. No side effects result from calling this tool.

From the tool's definition Tool name is 'estimate-fee-per-gas' and description states it 'estimate[s] for the fees per gas (in wei) for a transaction to be likely included in the next block' — this retrieves/queries blockchain state (current gas price estimates) with no side effects,…

Documented attack patterns abuse exactly the kind of access estimate-fee-per-gas gives an agent:

POLICY

How to control estimate-fee-per-gas

PolicyLayer is an MCP gateway — it sits between your AI agents and MetaMask MCP, and nothing reaches the server without passing your rules. This is the rule we recommend for estimate-fee-per-gas:

policy.json

{
  "version": "1",
  "default": "deny",
  "tools": {
    "estimate-fee-per-gas": {}
  }
}

estimate-fee-per-gas 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 MetaMask MCP — nothing to install.
Add this policy — paste it, or build it visually.
Point your MCP client (Claude, Cursor, anything) at your gateway URL.

CAP THIS TOOL →

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EXPLORE

Related tools and policies

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Go deeper

The MCP Attack Database → Documented attack patterns against MCP deployments — and the policies that stop them.
Data exfiltration → How read access becomes an exfiltration channel when chained with untrusted content.
MCP token cost → What connecting this server costs in context-window tokens on every request.
Rate Limiting MCP Tool Calls: A Practical Guide →
MCP Security: Why Prompt Guardrails Aren't Enough →

FAQ

Questions about estimate-fee-per-gas

What does the estimate-fee-per-gas tool do? +

Estimate for the fees per gas (in wei) for a transaction to be likely included in the next block. It is categorised as a Read tool in the MetaMask MCP MCP Server, which means it retrieves data without modifying state.

How do I enforce a policy on estimate-fee-per-gas? +

Register the MetaMask MCP server in PolicyLayer and add a rule for estimate-fee-per-gas: 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 MetaMask MCP. Nothing to install.

What risk level is estimate-fee-per-gas? +

estimate-fee-per-gas is a Read tool with low risk. Read-only tools are generally safe to allow by default.

Can I rate-limit estimate-fee-per-gas? +

Yes. Add a rate_limit block to the estimate-fee-per-gas 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 estimate-fee-per-gas completely? +

Set action: deny in the PolicyLayer policy for estimate-fee-per-gas. 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 estimate-fee-per-gas? +

estimate-fee-per-gas is provided by the MetaMask MCP server (xiawpohr/metamask-mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.

Enforce policy on every MetaMask MCP tool call.

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

CHECK YOUR STACK →