add_field · QGIS MCP: Risk & Policy

WHAT IT DOES

What add_field does on QGIS MCP

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

WHY IT NEEDS A POLICY

Why add_field needs a policy

This tool adds a field to a vector layer, which is a reversible modification of data structure. It does not execute arbitrary code, delete data irreversibly, or move money. The Write category applies because it creates new metadata/schema within the GIS project.

From the tool's definition Tool description states 'Add a new field to a vector layer' — this creates a new data structure within the layer, modifying the schema reversibly.

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

add_field Rate-limited

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.

View as policy code

policy.json

{
  "version": "1",
  "default": "deny",
  "tools": {
    "add_field": {
      "limits": [
        {
          "counter": "add_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 QGIS MCP, so you can run agents against it safely.

FAQ

Questions about add_field

What does the add_field tool do? +

Add a new field to a vector layer. field_type:. It is categorised as a Write tool in the QGIS MCP MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.

How do I enforce a policy on add_field? +

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

What risk level is add_field? +

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

Can I rate-limit add_field? +

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

Set action: deny in the PolicyLayer policy for 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 add_field? +

add_field is provided by the QGIS MCP server (nkarasiak/qgis-mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.