heim_start · Heim MCP: Risk & Policy

WHAT IT DOES

What heim_start does on Heim MCP

AI agents invoke heim_start to trigger actions in Heim MCP. 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 heim_start needs a policy

This tool executes/starts a runtime environment rather than simply reading or writing data. While not destructive in itself, starting a runtime can have significant side effects: it activates backend services, potentially making them accessible, consuming resources, and executing application code.

From the tool's definition Tool description states it 'Starts the Heim runtime which will run your backend applications' — this triggers external operations (runtime startup) whose effects depend on the state of deployed applications and system configuration.

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

heim_start Rate-limited

heim_start 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": {
    "heim_start": {
      "limits": [
        {
          "counter": "heim_start_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 Heim MCP, so you can run agents against it safely.

FAQ

Questions about heim_start

What does the heim_start tool do? +

Starts the Heim runtime which will run your backend applications. It is categorised as a Execute tool in the Heim MCP MCP Server, which means it can trigger actions or run processes. Use rate limits and argument validation.

How do I enforce a policy on heim_start? +

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

What risk level is heim_start? +

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

Can I rate-limit heim_start? +

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

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

heim_start is provided by the Heim MCP server (nor2-io/heim-mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.