fm_add_field

THE RISK

Medium Risk

Why fm_add_field needs a policy

Adding a field to a table is a write operation that modifies the database schema reversibly. While it alters structure rather than data, it is not destructive (fields can be removed) and does not execute arbitrary code or trigger side effects beyond the schema change itself.

From the tool's definition Tool description states 'Add a new field to an existing FileMaker table.' This is a schema modification operation that creates new data structure elements.

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

POLICY

How to control fm_add_field

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

policy.json

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

fm_add_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.

Create a free account and register Filemaker — nothing to install.
Add this policy — paste it, or build it visually.
Point your MCP client (Claude, Cursor, anything) at your gateway URL.

LIMIT THIS TOOL →

Free to start. No card required.

EXPLORE

Related tools and policies

More Filemaker tools

Destructive fm_delete_record Delete a FileMaker record by ROWID. Destructive fm_cleanup_test_data Deletes all test records marked with a specific tag. tagField must be an existing text fie Execute fm_run_script Run a FileMaker script. Returns scriptResult with code and resultParameter. Execute fm_run_script_and_assert Runs a FileMaker script and checks whether the result code matches the expected value. Execute fm_run_script_with_globals Sets global fields and runs a script in the SAME Data API session. This makes scripts that Write fm_create_record Create a new record in a FileMaker table. Write fm_create_table Create a new table in the FileMaker database (schema modification via OData). Write fm_create_test_record Creates a test record with a test tag. tagField must be an existing text field in the FM t

All 19 Filemaker tools →

Write 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.
Argument validation → Checking tool call arguments against schema and policy before they run.
Scoped token → Per-person credentials that grant a defined subset of servers and tools.
Rate Limiting MCP Tool Calls: A Practical Guide →
MCP Security: Why Prompt Guardrails Aren't Enough →

FAQ

Questions about fm_add_field

What does the fm_add_field tool do? +

Add a new field to an existing FileMaker table. SQL-style field types: VARCHAR(n), INT, NUMERIC, DATE, TIME, TIMESTAMP, BLOB. It is categorised as a Write tool in the Filemaker MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.

How do I enforce a policy on fm_add_field? +

Register the Filemaker MCP server in PolicyLayer and add a rule for fm_add_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 Filemaker. Nothing to install.

What risk level is fm_add_field? +

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

Can I rate-limit fm_add_field? +

Yes. Add a rate_limit block to the fm_add_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 fm_add_field completely? +

Set action: deny in the PolicyLayer policy for fm_add_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 fm_add_field? +

fm_add_field is provided by the Filemaker MCP server (joergkoester/mcp-server-filemaker). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.

Enforce policy on every Filemaker tool call.

Start from Filemaker, add the rest of your stack, and see everything your agents can call. Then put policy on all of it.

CHECK YOUR STACK →