AI agents call cast_balance to retrieve information from Foundry MCP Server without modifying anything — typically the context-gathering step in research, monitoring, and reporting workflows, before the agent takes action elsewhere.
This tool retrieves balance data from the blockchain without modifying, executing code, deleting, or moving funds. It is a read-only query operation, making it the lowest-risk category. Even in a misused context, an AI agent can only view balance information, not perform any consequential actions.
From the tool's definition Tool name is 'cast_balance' and description states 'Check the ETH balance of an address' — a pure query operation with no side effects.
Documented attack patterns abuse exactly the kind of access cast_balance gives an agent:
PolicyLayer is an MCP gateway — it sits between your AI agents and Foundry MCP Server, and nothing reaches the server without passing your rules. This is the rule we recommend for cast_balance:
{
"version": "1",
"default": "deny",
"tools": {
"cast_balance": {}
}
}cast_balance is read-only, so it stays allowed — but everything else on the server is denied unless you say otherwise.
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Check the ETH balance of an address. It is categorised as a Read tool in the Foundry MCP Server MCP Server, which means it retrieves data without modifying state.
Register the Foundry MCP Server MCP server in PolicyLayer and add a rule for cast_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 Foundry MCP Server. Nothing to install.
cast_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 cast_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 cast_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.
cast_balance is provided by the Foundry MCP Server MCP server (praneshasp/foundry-mcp-server). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
Deterministic rules across all 16 Foundry MCP Server tools. Per-identity grants. Full audit log. Live in minutes. Nothing to install.
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16 Foundry MCP Server tools catalogued and risk-classified — across an index of 42,500+ MCP servers.