call_service
Call any Home Assistant service. E.g. domain='light', service='turn_on', data={'entity_id':'light.living_room','brightness':200}.
This record as markdown: /tools/fistacho-ha-nexus-agent/call-service.md
What call_service does on Ha Nexus Agent
AI agents invoke call_service to trigger actions in Ha Nexus Agent. 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 call_service is rated High
This tool is a universal dispatcher that can invoke any Home Assistant service, including destructive actions (e.g., disabling security systems, unlocking doors, turning off alarms), automation triggers, and device control. Because it accepts arbitrary domain/service/data arguments, its blast radius encompasses the entire smart home — locks, alarms, climate, lighting, switches, and more.
From the tool's definition "Call any Home Assistant service" with arbitrary domain/service/data parameters — triggers external operations across all 202 tools/21 domains of a smart home system
Attacks that exploit this kind of access
The rule that runs call_service safely
PolicyLayer is an MCP gateway: it sits between your AI agents and Ha Nexus Agent, and checks every tool call against a rule you set before the call runs. Nothing changes on the server itself. For call_service, this is the rule to start with:
call_service 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.
The button opens the PolicyLayer dashboard: create your workspace, connect Ha Nexus Agent, apply this rule, and every call_service call is checked against it from then on.
Questions about call_service
Call any Home Assistant service. E.g. domain='light', service='turn_on', data={'entity_id':'light.living_room','brightness':200}. It is categorised as a Execute tool in the Ha Nexus Agent MCP Server, which means it can trigger actions or run processes. Use rate limits and argument validation.
Register the Ha Nexus Agent MCP server in PolicyLayer and add a rule for call_service: 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 Ha Nexus Agent. Nothing to install.
call_service is a Execute tool with high risk. Execute tools should be rate-limited and have argument validation enabled.
Yes. Add a rate_limit block to the call_service 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 call_service. 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.
call_service is provided by the Ha Nexus Agent MCP server (fistacho/ha-nexus-agent). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
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