open_spi · Buspirate MCP: Risk & Policy

WHAT IT DOES

What open_spi does on Buspirate

AI agents use open_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 open_spi needs a policy

This tool initializes/opens an SPI hardware connection on the BusPirate device. It creates a new connection state rather than reading data or executing commands on the target. It is reversible (can be closed via close_spi). No data is written to a target device yet, but it does establish an active hardware interface. 'Write' fits best as it creates/modifies state on the hardware testing device.

From the tool's definition Open an SPI connection and start an engagement

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

open_spi Rate-limited

open_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": {
    "open_spi": {
      "limits": [
        {
          "counter": "open_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 open_spi

What does the open_spi tool do? +

Open an SPI connection and start an engagement. 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 open_spi? +

Register the Buspirate MCP server in PolicyLayer and add a rule for open_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 open_spi? +

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

Can I rate-limit open_spi? +

Yes. Add a rate_limit block to the open_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 open_spi completely? +

Set action: deny in the PolicyLayer policy for open_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 open_spi? +

open_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.