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ruff-check

Runs ruff check and returns structured lint diagnostics (file, line, code, message).

How to control ruff-check ↓

What ruff-check does on Lint

AI agents invoke ruff-check to trigger actions in Lint. 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.

High Risk

Why ruff-check needs a policy

The tool executes an external linting process (ruff check) on files. While it is primarily a read/analysis operation, it runs an external command/tool which qualifies as Execute. The blast radius is medium since it runs code analysis on files but doesn't modify or delete them; however, it could be misused to analyze sensitive files or consume resources.

From the tool's definition Runs ruff check and returns structured lint diagnostics

Documented attack patterns abuse exactly the kind of access ruff-check gives an agent:

How to control ruff-check

PolicyLayer is an MCP gateway — it sits between your AI agents and Lint, and nothing reaches the server without passing your rules. This is the rule we recommend for ruff-check:

policy.json
{
  "version": "1",
  "default": "deny",
  "tools": {
    "ruff-check": {
      "limits": [
        {
          "counter": "ruff-check_rate",
          "window": "minute",
          "max": 10,
          "scope": "grant"
        }
      ]
    }
  }
}

ruff-check 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.

  1. Create a free account and register Lint — nothing to install.
  2. Add this policy — paste it, or build it visually.
  3. Point your MCP client (Claude, Cursor, anything) at your gateway URL.
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Related tools and policies

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Questions about ruff-check

What does the ruff-check tool do? +

Runs ruff check and returns structured lint diagnostics (file, line, code, message). It is categorised as a Execute tool in the Lint MCP Server, which means it can trigger actions or run processes. Use rate limits and argument validation.

How do I enforce a policy on ruff-check? +

Register the Lint MCP server in PolicyLayer and add a rule for ruff-check: 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 Lint. Nothing to install.

What risk level is ruff-check? +

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

Can I rate-limit ruff-check? +

Yes. Add a rate_limit block to the ruff-check 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 ruff-check completely? +

Set action: deny in the PolicyLayer policy for ruff-check. 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 ruff-check? +

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

Enforce policy on every Lint tool call.

Start from Lint, add the rest of your stack, and see everything your agents can call. Then put policy on all of it.

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