create_custom_field · Mycase MCP: Risk & Policy

WHAT IT DOES

What create_custom_field does on Mycase

AI agents use create_custom_field to create or update resources in Mycase — usually the action step of a workflow, after the agent has gathered context. Every call changes real data in your Mycase environment.

WHY IT NEEDS A POLICY

Why create_custom_field needs a policy

This tool creates new metadata/field definitions in the law firm's case management system. It modifies the system schema reversibly (custom fields can be deleted or modified later), which qualifies it as Write rather than Execute. The severity is medium because misuse could clutter the system with unwanted fields or expose sensitive field structures, but the impact is reversible and limited to configuration.

From the tool's definition "Create a custom field" with parameters for parent_type and field_type indicates the tool creates new data structures within the MyCase system. The description explicitly states it creates custom fields that persist in the database.

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

create_custom_field Rate-limited

create_custom_field stays usable, but capped — an agent stuck in a loop can't make hundreds of changes a minute. Everything else on the server is denied unless you say otherwise.

View as policy code

policy.json

{
  "version": "1",
  "default": "deny",
  "tools": {
    "create_custom_field": {
      "limits": [
        {
          "counter": "create_custom_field_rate",
          "window": "minute",
          "max": 30,
          "scope": "grant"
        }
      ]
    }
  }
}

LIMIT THIS TOOL →

Instant setup, no code required.

PolicyLayer is an MCP gateway: every tool call is checked against your rule before it reaches Mycase, so you can run agents against it safely.

FAQ

Questions about create_custom_field

What does the create_custom_field tool do? +

Create a custom field. parent_type: Case|Client|Lead. field_type: text|date|list|checkbox|number. list_options: comma-separated option values for list type fields (e.g. 'Option A,Option B,Option C'). It is categorised as a Write tool in the Mycase MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.

How do I enforce a policy on create_custom_field? +

Register the Mycase MCP server in PolicyLayer and add a rule for create_custom_field: 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 Mycase. Nothing to install.

What risk level is create_custom_field? +

create_custom_field is a Write tool with medium risk. Write tools should be rate-limited to prevent accidental bulk modifications.

Can I rate-limit create_custom_field? +

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

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

create_custom_field is provided by the Mycase MCP server (rosenadvertising/mycase-mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.