erc20_balanceOf

THE RISK

Low Risk

Why erc20_balanceOf needs a policy

This tool performs a read-only operation on a blockchain to fetch token balance information. It does not modify state, execute code, delete data, or move funds. The blast radius of misuse is minimal—an attacker could only enumerate wallet balances, which is already public blockchain data. This is a straightforward Read category tool.

From the tool's definition Tool name 'erc20_balanceOf' and description 'Get the ERC20 token balance for a specific address' indicate a query operation that retrieves data without side effects.

Documented attack patterns abuse exactly the kind of access erc20_balanceOf gives an agent:

POLICY

How to control erc20_balanceOf

PolicyLayer is an MCP gateway — it sits between your AI agents and MCP Ethers Wallet, and nothing reaches the server without passing your rules. This is the rule we recommend for erc20_balanceOf:

policy.json

{
  "version": "1",
  "default": "deny",
  "tools": {
    "erc20_balanceOf": {}
  }
}

erc20_balanceOf 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 MCP Ethers Wallet — 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

Related tools and policies

More MCP Ethers Wallet tools

Financial prepareERC1155BatchTransfer Prepare an ERC1155 batch transfer transaction for signing. Returns transaction data that c Financial safeBatchTransferERC1155 Safely transfer multiple tokens from the connected wallet to another address in a single t Financial safeTransferERC1155 Safely transfer tokens from the connected wallet to another address Financial safeTransferERC721 Safely transfer an NFT from the connected wallet to another address, with additional data Financial transferERC20 Transfer ERC20 tokens from the connected wallet to another address Financial transferERC721 Transfer an NFT from the connected wallet to another address Financial transferFromERC20 Transfer ERC20 tokens from one address to another (requires approval) Financial transferNFT transferNFT

All 69 MCP Ethers Wallet tools →

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Go deeper

Roll out MCP under one policy → Per-person scoped tokens, one central policy, and full audit across every server your team connects.
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 →
PolicyLayer vs alternatives → How deterministic, per-call MCP policy compares with gateways, identity layers, and authorisation platforms.

FAQ

Questions about erc20_balanceOf

What does the erc20_balanceOf tool do? +

Get the ERC20 token balance for a specific address. Alternative naming for compatibility with MCP client tests. It is categorised as a Read tool in the MCP Ethers Wallet MCP Server, which means it retrieves data without modifying state.

How do I enforce a policy on erc20_balanceOf? +

Register the MCP Ethers Wallet MCP server in PolicyLayer and add a rule for erc20_balanceOf: 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 MCP Ethers Wallet. Nothing to install.

What risk level is erc20_balanceOf? +

erc20_balanceOf is a Read tool with low risk. Read-only tools are generally safe to allow by default.

Can I rate-limit erc20_balanceOf? +

Yes. Add a rate_limit block to the erc20_balanceOf 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 erc20_balanceOf completely? +

Set action: deny in the PolicyLayer policy for erc20_balanceOf. 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 erc20_balanceOf? +

erc20_balanceOf is provided by the MCP Ethers Wallet MCP server (crazyrabbitltc/mcp-ethers-server). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.

Enforce policy on every MCP Ethers Wallet tool call.

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

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