Live native + ERC-20 token balances for an EVM address (Base, Ethereum, Polygon, Arbitrum, Optimism; keyless). Returns the native-coin balance and, for any ERC-20 contract addresses you pass, the symbol, decimals, raw and human-formatted balance — fetched in one multicall. For wallet dashboards, ...
AI agents call crypto.balances to retrieve information from Mcp without modifying anything — typically the context-gathering step in research, monitoring, and reporting workflows, before the agent takes action elsewhere.
This tool queries and retrieves cryptocurrency balance information from blockchain addresses without creating, modifying, or deleting any data. It is a straightforward data retrieval operation with no side effects.
From the tool's definition Tool description states it 'Returns the native-coin balance and... token balances — fetched in one multicall' with no modification capability mentioned.
Attacks that exploit this kind of access
Live native + ERC-20 token balances for an EVM address (Base, Ethereum, Polygon, Arbitrum, Optimism; keyless). Returns the native-coin balance and, for any ERC-20 contract addresses you pass, the symbol, decimals, raw and human-formatted balance — fetched in one multicall. For wallet dashboards, treasury checks, and ag. It is categorised as a Read tool in the Mcp MCP Server, which means it retrieves data without modifying state.
Register the MCP server in PolicyLayer and add a rule for crypto.balances: 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. Nothing to install.
crypto.balances 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 crypto.balances 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 crypto.balances. 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.
crypto.balances is provided by the MCP server (@2sio/mcp). 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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