contract_call · Hedera Toolbox MCP: Risk & Policy

WHAT IT DOES

What contract_call does on Hedera Toolbox

AI agents invoke contract_call to trigger actions in Hedera Toolbox. What it does depends on the arguments the agent supplies, and its effects often reach beyond the immediate call — builds kicked off, notifications sent, workflows started.

WHY IT NEEDS A POLICY

Why contract_call needs a policy

This tool invokes smart contract execution on a live blockchain network. Although the description indicates read-only semantics, contract functions can perform observable state queries and potentially interact with other contracts or protocols.

From the tool's definition Tool name 'contract_call' and description 'Execute a read-only call to a Hedera smart contract function' explicitly state execution of smart contract code.

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

contract_call Rate-limited

contract_call stays usable, but rate-capped — a runaway agent can't fire it dozens of times a minute. Everything else on the server is denied unless you say otherwise.

View as policy code

policy.json

{
  "version": "1",
  "default": "deny",
  "tools": {
    "contract_call": {
      "limits": [
        {
          "counter": "contract_call_rate",
          "window": "minute",
          "max": 10,
          "scope": "grant"
        }
      ]
    }
  }
}

RATE-LIMIT THIS TOOL →

Instant setup, no code required.

PolicyLayer is an MCP gateway: every tool call is checked against your rule before it reaches Hedera Toolbox, so you can run agents against it safely.

FAQ

Questions about contract_call

What does the contract_call tool do? +

Execute a read-only call to a Hedera smart contract function and return the. It is categorised as a Execute tool in the Hedera Toolbox MCP Server, which means it can trigger actions or run processes. Use rate limits and argument validation.

How do I enforce a policy on contract_call? +

Register the Hedera Toolbox MCP server in PolicyLayer and add a rule for contract_call: 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 Hedera Toolbox. Nothing to install.

What risk level is contract_call? +

contract_call is a Execute tool with high risk. Execute tools should be rate-limited and have argument validation enabled.

Can I rate-limit contract_call? +

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

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

contract_call is provided by the Hedera Toolbox MCP server (mountainmystic/hederatoolbox). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.