i2c_write · Buspirate MCP: Risk & Policy

WHAT IT DOES

What i2c_write does on Buspirate

AI agents use i2c_write to create or update resources in Buspirate — usually the action step of a workflow, after the agent has gathered context. Every call changes real data in your Buspirate environment.

WHY IT NEEDS A POLICY

Why i2c_write needs a policy

This tool creates or modifies data on connected hardware by writing to I2C registers. While reversible in principle (registers can be rewritten), misuse could corrupt device state, disable safety features, or cause hardware malfunction. It is not Destructive because writes are typically reversible, but it merits high severity due to potential hardware damage and lack of user confirmation.

From the tool's definition Tool name 'i2c_write' and description 'Write bytes to an I2C device register' indicate data modification to hardware devices via the I2C protocol.

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

i2c_write Rate-limited

i2c_write 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": {
    "i2c_write": {
      "limits": [
        {
          "counter": "i2c_write_rate",
          "window": "minute",
          "max": 30,
          "scope": "grant"
        }
      ]
    }
  }
}

LIMIT THIS TOOL →

Instant setup, no code required.

PolicyLayer is an MCP gateway: every tool call is checked against your rule before it reaches Buspirate, so you can run agents against it safely.

FAQ

Questions about i2c_write

What does the i2c_write tool do? +

Write bytes to an I2C device register. It is categorised as a Write tool in the Buspirate MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.

How do I enforce a policy on i2c_write? +

Register the Buspirate MCP server in PolicyLayer and add a rule for i2c_write: 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 Buspirate. Nothing to install.

What risk level is i2c_write? +

i2c_write is a Write tool with medium risk. Write tools should be rate-limited to prevent accidental bulk modifications.

Can I rate-limit i2c_write? +

Yes. Add a rate_limit block to the i2c_write 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 i2c_write completely? +

Set action: deny in the PolicyLayer policy for i2c_write. 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 i2c_write? +

i2c_write is provided by the Buspirate MCP server (mplogas/buspirate-mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.