preview_server

THE RISK

High Risk

Why preview_server needs a policy

Starting a local server is an Execute action: it runs an external operation whose effects depend on arguments (port number, document path, etc.) and cannot be trivially undone without stopping the process. It is not Destructive (no data loss), Write (not creating/modifying persistent data), or Read (actively initiates a process).

From the tool's definition Tool description states 'Start a local preview server' — this initiates a process/server, which is an external operation with side effects (binding ports, resource allocation, network listeners).

Documented attack patterns abuse exactly the kind of access preview_server gives an agent:

POLICY

How to control preview_server

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

policy.json

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

preview_server 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.

Create a free account and register Quarkdown MCP Server — nothing to install.
Add this policy — paste it, or build it visually.
Point your MCP client (Claude, Cursor, anything) at your gateway URL.

RATE-LIMIT THIS TOOL →

Free to start. No card required.

EXPLORE

Related tools and policies

More Quarkdown MCP Server tools

Execute compile_document Compile Quarkdown source content to various output formats (HTML, PDF, LaTeX, Markdown) Execute convert_batch Convert multiple Quarkdown documents in batch mode with consistent settings Write create_project Create a new Quarkdown project with proper directory structure and template files Read validate_markdown Validate Quarkdown document syntax and report any errors or warnings

All 5 Quarkdown MCP Server tools →

Execute tools on other servers

Android Forensics ADB MCP Server adb_shell_command EMBA-MCP run_emba_scan Frida Game Hacking MCP remove_breakpoint Procmon request_elevation

Go deeper

High-risk tools in Quarkdown MCP Server → Every high-risk tool this server exposes, in one view.
All high-risk MCP tools → Every high-risk tool across the catalogue, and the policy pattern that contains them.
The MCP Attack Database → Documented attack patterns against MCP deployments — and the policies that stop them.
Agent sandbox → Bounding what an agent can execute and where the boundary should sit.
Least privilege for MCP → Granting agents the minimum tool surface the task needs.
Rate Limiting MCP Tool Calls: A Practical Guide →
MCP Security: Why Prompt Guardrails Aren't Enough →

FAQ

Questions about preview_server

What does the preview_server tool do? +

Start a local preview server for Quarkdown documents with live reload. It is categorised as a Execute tool in the Quarkdown MCP Server 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_server? +

Register the Quarkdown MCP Server MCP server in PolicyLayer and add a rule for preview_server: 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 Quarkdown MCP Server. Nothing to install.

What risk level is preview_server? +

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

Can I rate-limit preview_server? +

Yes. Add a rate_limit block to the preview_server 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_server completely? +

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

preview_server is provided by the Quarkdown MCP Server MCP server (lillard01/quarkdown-mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.

Enforce policy on every Quarkdown MCP Server tool call.

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

CHECK YOUR STACK →