fmt · Python MCP: Risk & Policy

WHAT IT DOES

What fmt does on Python

AI agents invoke fmt to trigger actions in Python. 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 IT NEEDS A POLICY

Why fmt needs a policy

The tool runs a formatter (likely rustfmt) that can either check or fix Rust code formatting. In 'fix' mode it modifies source files in place, making it a Write/Execute operation. Since it runs an external tool and can overwrite file contents, Execute is the most appropriate category. Severity is medium because misuse could reformat or alter source code, though changes are typically reversible via version control.

From the tool's definition 'fixes Rust formatting' — the tool can modify source files by applying formatting changes

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

fmt Rate-limited

fmt 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.

View as policy code

policy.json

{
  "version": "1",
  "default": "deny",
  "tools": {
    "fmt": {
      "limits": [
        {
          "counter": "fmt_rate",
          "window": "minute",
          "max": 10,
          "scope": "grant"
        }
      ]
    }
  }
}

RATE-LIMIT THIS TOOL →

Instant setup, no code required.

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

FAQ

Questions about fmt

What does the fmt tool do? +

Checks or fixes Rust formatting and returns structured output. It is categorised as a Execute tool in the Python MCP Server, which means it can trigger actions or run processes. Use rate limits and argument validation.

How do I enforce a policy on fmt? +

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

What risk level is fmt? +

fmt is a Execute tool with high risk. Execute tools should be rate-limited and have argument validation enabled.

Can I rate-limit fmt? +

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

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

fmt is provided by the Python MCP server (Dave-London/Pare). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.

// THE FULL RECORD

fmt is one line of Python's registry record.

The record carries the whole server: verified identity, auth posture, risk grade, every tool classified, recommended policy — re-checked continuously.

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