list_custom_fields

THE RISK

Low Risk

Why list_custom_fields needs a policy

This is a straightforward read operation that retrieves metadata about user-defined custom fields. It queries collection metadata without creating, modifying, or deleting anything. The blast radius of misuse is minimal—an AI agent could only enumerate field definitions, which poses no security or privacy risk beyond reading what already exists in the user's account.

From the tool's definition The tool lists custom fields but does not modify, delete, or execute operations. The verb 'list' and the description 'List all custom fields defined in your Discogs collection' indicate pure data retrieval with no side effects.

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

POLICY

How to control list_custom_fields

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

policy.json

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

list_custom_fields 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 Discogs 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.

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EXPLORE

Related tools and policies

More Discogs MCP Server tools

Destructive delete_folder Delete a folder from your Discogs collection. The folder must be empty (no releases). Cann Destructive remove_from_collection Remove a specific release instance from a folder in your Discogs collection. Use search_co Execute refresh_collection Force an immediate full refresh of the cached collection snapshot. Use after adding or rem Write rate_release Rate a release in your Discogs collection from 0 (no rating) to 5 stars. Use search_collec Write add_to_collection Add a release to a folder in your Discogs collection. If no folder is specified, adds to t Write create_folder Create a new folder in your Discogs collection for organizing releases. Write edit_custom_field Set a custom field value on a release in your Discogs collection. Use list_custom_fields t Write edit_folder Rename an existing folder in your Discogs collection. Cannot rename the system folders (Al

All 20 Discogs MCP Server tools →

Read tools on other servers

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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 list_custom_fields

What does the list_custom_fields tool do? +

List all custom fields defined in your Discogs collection. Custom fields allow you to add metadata like notes, tags, or categories to releases. It is categorised as a Read tool in the Discogs MCP Server MCP Server, which means it retrieves data without modifying state.

How do I enforce a policy on list_custom_fields? +

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

What risk level is list_custom_fields? +

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

Can I rate-limit list_custom_fields? +

Yes. Add a rate_limit block to the list_custom_fields 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_fields completely? +

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

list_custom_fields is provided by the Discogs MCP Server MCP server (rianvdm/discogs-mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.

Enforce policy on every Discogs MCP Server tool call.

Start from Discogs 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 →