AI agents call list_custom_fields to retrieve information from Keycrm without modifying anything — typically the context-gathering step in research, monitoring, and reporting workflows, before the agent takes action elsewhere.
This tool retrieves metadata about custom field configurations from keyCRM. It queries and returns data (IDs, names, types, allowed values) without creating, modifying, deleting, or executing any operations. The blast radius of misuse is minimal—an attacker could learn the schema of custom fields but cannot alter data or trigger external actions. This is a straightforward Read operation.
From the tool's definition Tool name 'list_custom_fields' and description 'List all custom fields' indicate a retrieval operation with no modification or side effects.
Attacks that exploit this kind of access
List all custom fields configured in keyCRM with their IDs, names, types, and allowed values. It is categorised as a Read tool in the Keycrm MCP Server, which means it retrieves data without modifying state.
Register the Keycrm 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 Keycrm. Nothing to install.
list_custom_fields is a Read tool with low risk. Read-only tools are generally safe to allow by default.
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.
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.
list_custom_fields is provided by the Keycrm MCP server (ivanklymenko/keycrm-mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
Every MCP server has a record like this.
Type a name, get the same breakdown: verified identity, auth posture, risk grade, capabilities, recommended policy.
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