AI agents call custom_field_list to retrieve information from Ashby MCP without modifying anything — typically the context-gathering step in research, monitoring, and reporting workflows, before the agent takes action elsewhere.
This tool queries and returns metadata about custom fields in the Ashby organization without creating, modifying, or deleting any data. It is a straightforward read operation with minimal blast radius if misused by an AI agent.
From the tool's definition Tool name includes 'list' and description states 'List all custom fields' — a retrieval operation with no modification or side effects.
Attacks that exploit this kind of access
List all custom fields defined in the organization. It is categorised as a Read tool in the Ashby MCP MCP Server, which means it retrieves data without modifying state.
Register the Ashby MCP server in PolicyLayer and add a rule for custom_field_list: 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 Ashby MCP. Nothing to install.
custom_field_list 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 custom_field_list 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 custom_field_list. 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.
custom_field_list is provided by the Ashby MCP server (jaketeagle/ashby-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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