template_render · Homeassistant MCP: Risk & Policy

WHAT IT DOES

What template_render does on Homeassistant

AI agents invoke template_render to trigger actions in Homeassistant. 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 template_render needs a policy

In Home Assistant, template rendering executes Jinja2 template expressions that can evaluate arbitrary logic, access entity states, and potentially trigger side effects. The 'render' verb implies execution of code/expressions rather than a simple read or write. Empty description lowers confidence, but the known Home Assistant template engine behavior makes Execute the most likely and most severe applicable category.

From the tool's definition Tool name 'template_render' on a Home Assistant MCP server; description is empty and uninformative.

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

template_render Rate-limited

template_render 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": {
    "template_render": {
      "limits": [
        {
          "counter": "template_render_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 Homeassistant, so you can run agents against it safely.

FAQ

Questions about template_render

What does the template_render tool do? +

template_render. It is categorised as a Execute tool in the Homeassistant MCP Server, which means it can trigger actions or run processes. Use rate limits and argument validation.

How do I enforce a policy on template_render? +

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

What risk level is template_render? +

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

Can I rate-limit template_render? +

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

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

template_render is provided by the Homeassistant MCP server (robbrad/homeassistant-mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.