list_custom_patterns

THE RISK

Low Risk

Why list_custom_patterns needs a policy

This tool reads and returns configuration data about custom CSS patterns. It performs a simple lookup or enumeration of existing patterns without creating, modifying, deleting, or executing any operations. The verb 'list' is characteristic of Read category tools. The blast radius is minimal—the worst case is information disclosure about the user's CSS configuration, which is low-severity data exposure.

From the tool's definition Tool name 'list_custom_patterns' and description 'List all custom (user-defined) patterns loaded from your config file' indicate a retrieval/query operation with no side effects.

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

POLICY

How to control list_custom_patterns

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

policy.json

{
  "version": "1",
  "default": "deny",
  "tools": {
    "list_custom_patterns": {}
  }
}

list_custom_patterns is read-only, so it stays allowed — but everything else on the server is denied unless you say otherwise.

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

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EXPLORE

Related tools and policies

More Classmcp tools

Execute reload_config Reload custom patterns from the config file (.classmcp.json). Use this after modifying you Write generate_css Generate CSS that defines all semantic classes. Add this to your project Write set_framework Set the CSS framework to use for all subsequent operations. Choose based on your project Read get_class Get the full utility classes for a semantic class name. Returns the CSS classes you should Read get_component Get a complete HTML component example using semantic classes. Great for seeing how classes Read get_ssr_info Get SSR/hydration safety information for a class pattern. Use this when building SSR/Next. Read list_classes List all available semantic class names, optionally filtered by category. Use this to disc Read list_frameworks List all available CSS frameworks and their statistics.

All 10 Classmcp tools →

Read tools on other servers

M-Team MCP Server get_torrent_detail YouTube MCP Server search_channel Android Forensics ADB MCP Server parse_browser_history 0xarchive web3_challenge

Go deeper

The MCP Attack Database → Documented attack patterns against MCP deployments — and the policies that stop them.
Data exfiltration → How read access becomes an exfiltration channel when chained with untrusted content.
MCP token cost → What connecting this server costs in context-window tokens on every request.
Rate Limiting MCP Tool Calls: A Practical Guide →
MCP Security: Why Prompt Guardrails Aren't Enough →

FAQ

Questions about list_custom_patterns

What does the list_custom_patterns tool do? +

List all custom (user-defined) patterns loaded from your config file. It is categorised as a Read tool in the Classmcp MCP Server, which means it retrieves data without modifying state.

How do I enforce a policy on list_custom_patterns? +

Register the Class MCP server in PolicyLayer and add a rule for list_custom_patterns: 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 Classmcp. Nothing to install.

What risk level is list_custom_patterns? +

list_custom_patterns is a Read tool with low risk. Read-only tools are generally safe to allow by default.

Can I rate-limit list_custom_patterns? +

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

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

list_custom_patterns is provided by the Class MCP server (thedecipherist/classmcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.

Enforce policy on every Classmcp tool call.

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

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