preview_markdown · Markview MCP: Risk & Policy

WHAT IT DOES

What preview_markdown does on Markview

AI agents invoke preview_markdown to trigger actions in Markview. 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 preview_markdown needs a policy

The tool renders content in an external macOS application (MarkView), which constitutes triggering an external operation beyond simple data retrieval. While not destructive or financial, it actively causes a side effect by opening/updating a native viewer, classifying it as Execute. Severity is medium because a malicious agent could render arbitrary content in the viewer, though blast radius is limited.

From the tool's definition 'Render a markdown string in MarkView' — triggers an external operation in a native macOS viewer application

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

preview_markdown Rate-limited

preview_markdown 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": {
    "preview_markdown": {
      "limits": [
        {
          "counter": "preview_markdown_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 Markview, so you can run agents against it safely.

FAQ

Questions about preview_markdown

What does the preview_markdown tool do? +

Render a markdown string in MarkView. It is categorised as a Execute tool in the Markview MCP Server, which means it can trigger actions or run processes. Use rate limits and argument validation.

How do I enforce a policy on preview_markdown? +

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

What risk level is preview_markdown? +

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

Can I rate-limit preview_markdown? +

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

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

preview_markdown is provided by the Markview MCP server (mcp-server-markview). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.