write_config

Write ESPHome device YAML config to /config/esphome/. Validates YAML syntax before saving.

SERVERHa Nexus Agent SOURCEfistacho/ha-nexus-agent

Medium RISK CLASS

Category Write

Parameters 00 required

Recommended Rate-limitedsee the rule below

Registry record Grade F, identity unverified Pull the record →

This record as markdown: /tools/fistacho-ha-nexus-agent/write-config.md

WHAT IT DOES

What write_config does on Ha Nexus Agent

AI agents use write_config to create or update resources in Ha Nexus Agent, usually the action step of a workflow, after the agent has gathered context. Every call changes real data in your Ha Nexus Agent environment.

RISK

Why write_config is rated Medium

This is a Write operation—it creates or modifies device configuration files reversibly. Severity is high because ESPHome configs control embedded device behavior (sensors, actuators, automation logic); malicious configs could cause unintended device behavior, expose credentials, or compromise IoT security.

From the tool's definition Tool writes YAML configuration files to /config/esphome/ directory. Description states 'Write...config to /config/esphome/' with YAML validation before saving.

Attacks that exploit this kind of access

RECOMMENDED RULE

The rule that runs write_config 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 write_config, this is the rule to start with:

write_config Rate-limited

write_config stays usable, but capped: an agent stuck in a loop can't make hundreds of changes a minute. Everything else on the server is denied unless you say otherwise.

View as policy code

policy.json

{
  "version": "1",
  "default": "deny",
  "tools": {
    "write_config": {
      "limits": [
        {
          "counter": "write_config_rate",
          "window": "minute",
          "max": 30,
          "scope": "grant"
        }
      ]
    }
  }
}

LIMIT THIS TOOL → Instant setup, no code required.

The button opens the PolicyLayer dashboard: create your workspace, connect Ha Nexus Agent, apply this rule, and every write_config call is checked against it from then on.

FAQ

Questions about write_config

What does the write_config tool do? +

Write ESPHome device YAML config to /config/esphome/. Validates YAML syntax before saving. It is categorised as a Write tool in the Ha Nexus Agent MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.

How do I enforce a policy on write_config? +

Register the Ha Nexus Agent MCP server in PolicyLayer and add a rule for write_config: 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.

What risk level is write_config? +

write_config is a Write tool with medium risk. Write tools should be rate-limited to prevent accidental bulk modifications.

Can I rate-limit write_config? +

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

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

write_config 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.

KEEP EXPLORING

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