schema_list_classes

THE RISK

Low Risk

Why schema_list_classes needs a policy

This tool retrieves or enumerates metadata about available schema classes without creating, modifying, deleting, or executing any side effects. The deprecation notice and suggestion to use schema_query does not change its fundamental read-only nature.

From the tool's definition Tool name 'schema_list_classes' and description 'List all available classes in DEXPI or SFILES schemas' indicate a query/retrieval operation with no data modification capability.

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

POLICY

How to control schema_list_classes

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

policy.json

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

schema_list_classes 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 Engineering 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.

CAP THIS TOOL →

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EXPLORE

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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 schema_list_classes

What does the schema_list_classes tool do? +

[DEPRECATED] List all available classes in DEXPI or SFILES schemas. Use schema_query(operation=. It is categorised as a Read tool in the Engineering MCP Server MCP Server, which means it retrieves data without modifying state.

How do I enforce a policy on schema_list_classes? +

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

What risk level is schema_list_classes? +

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

Can I rate-limit schema_list_classes? +

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

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

schema_list_classes is provided by the Engineering MCP Server MCP server (puran-water/dexpi-sfiles-mcp-server). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.

Enforce policy on every Engineering MCP Server tool call.

Start from Engineering 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 →