update_field_metadata · Instant Db MCP: Risk & Policy

WHAT IT DOES

What update_field_metadata does on Instant Db

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

WHY IT NEEDS A POLICY

Why update_field_metadata needs a policy

This tool creates or modifies metadata associated with database columns. It is a Write operation because it updates column attributes (display name and description) in a reversible manner—these metadata changes can be updated or removed without data loss. It does not execute queries, delete data, or perform destructive operations.

From the tool's definition The tool modifies column metadata by setting display names and descriptions. The description states it 'Set[s] a display name and/or description on a column' and that 'Field metadata is returned by describe_database', indicating persistent changes to schema…

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

update_field_metadata Rate-limited

update_field_metadata 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": {
    "update_field_metadata": {
      "limits": [
        {
          "counter": "update_field_metadata_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 Instant Db, so you can run agents against it safely.

FAQ

Questions about update_field_metadata

What does the update_field_metadata tool do? +

Set a display name and/or description on a column. Use this to document what a field means, its valid values, units, or formatting rules. Field metadata is returned by describe_database. It is categorised as a Write tool in the Instant Db MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.

How do I enforce a policy on update_field_metadata? +

Register the Instant Db MCP server in PolicyLayer and add a rule for update_field_metadata: 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 Instant Db. Nothing to install.

What risk level is update_field_metadata? +

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

Can I rate-limit update_field_metadata? +

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

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

update_field_metadata is provided by the Instant Db MCP server (urbushey/mcp-db). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.