AI agents call eth_get_token_balance to retrieve information from PortalMCP without modifying anything — typically the context-gathering step in research, monitoring, and reporting workflows, before the agent takes action elsewhere.
This tool performs a simple data retrieval operation—querying the balance of an ERC-20 token at a given address. There are no side effects, no state modifications, no code execution, and no financial transactions. Even in the context of a blockchain/DeFi server, this is purely informational. The blast radius of misuse is minimal (information disclosure only). Classification as Read is appropriate.
From the tool's definition Tool name 'eth_get_token_balance' and description 'Get the balance of an ERC-20 token for a specific address' indicate a read-only query operation that retrieves data without modifying state or executing code.
Attacks that exploit this kind of access
Get the balance of an ERC-20 token for a specific address, or the default signer wallet if no address is provided. It is categorised as a Read tool in the PortalMCP MCP Server, which means it retrieves data without modifying state.
Register the Portal MCP server in PolicyLayer and add a rule for eth_get_token_balance: 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 PortalMCP. Nothing to install.
eth_get_token_balance is a Read tool with low risk. Read-only tools are generally safe to allow by default.
Yes. Add a rate_limit block to the eth_get_token_balance 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.
Set action: deny in the PolicyLayer policy for eth_get_token_balance. 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.
eth_get_token_balance is provided by the Portal MCP server (portalfnd/portalmcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
Every MCP server has a record like this.
Type a name, get the same breakdown: verified identity, auth posture, risk grade, capabilities, recommended policy.
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