close_spi · Buspirate MCP: Risk & Policy

WHAT IT DOES

What close_spi does on Buspirate

AI agents use close_spi 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 close_spi needs a policy

This tool closes an active SPI session and resets the BusPirate hardware to HiZ (high-impedance) mode. It modifies hardware state reversibly — the session can be reopened and the device reconfigured. It does not delete data or execute arbitrary commands, placing it in the Write category.

From the tool's definition 'Close an SPI session and reset the BusPirate to HiZ mode' — terminates a session and changes hardware state

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

close_spi Rate-limited

close_spi 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": {
    "close_spi": {
      "limits": [
        {
          "counter": "close_spi_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 close_spi

What does the close_spi tool do? +

Close an SPI session and reset the BusPirate to HiZ mode. [allowed-write] [Duration: instant.]. 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 close_spi? +

Register the Buspirate MCP server in PolicyLayer and add a rule for close_spi: 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 close_spi? +

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

Can I rate-limit close_spi? +

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

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

close_spi 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.