foundry_build · HashPilot MCP: Risk & Policy

WHAT IT DOES

What foundry_build does on HashPilot

AI agents invoke foundry_build to trigger actions in HashPilot. 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 foundry_build needs a policy

This tool invokes the Foundry compiler (foundry_build) to compile Solidity contracts and write artifacts to disk. While compilation itself is deterministic and reversible (artifacts can be deleted), it is an Execute category tool because it runs an external code transformation process whose effects persist on the file system.

From the tool's definition Compile all Solidity contracts in the project. Significantly faster than Hardhat (3-4x). Generates artifacts in out/ directory.

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

foundry_build Rate-limited

foundry_build 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": {
    "foundry_build": {
      "limits": [
        {
          "counter": "foundry_build_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 HashPilot, so you can run agents against it safely.

FAQ

Questions about foundry_build

What does the foundry_build tool do? +

Compile all Solidity contracts in the project. Significantly faster than Hardhat (3-4x). Generates artifacts in out/ directory. It is categorised as a Execute tool in the HashPilot MCP Server, which means it can trigger actions or run processes. Use rate limits and argument validation.

How do I enforce a policy on foundry_build? +

Register the HashPilot MCP server in PolicyLayer and add a rule for foundry_build: 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 HashPilot. Nothing to install.

What risk level is foundry_build? +

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

Can I rate-limit foundry_build? +

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

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

foundry_build is provided by the HashPilot MCP server (justmert/hashpilot). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.