set_project_variable · QGIS MCP: Risk & Policy

WHAT IT DOES

What set_project_variable does on QGIS MCP

AI agents use set_project_variable 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 set_project_variable needs a policy

This is a Write operation because it creates or modifies project state reversibly. While not directly destructive, it can affect project behavior and expressions globally. Severity is medium because misuse could corrupt project logic or introduce subtle calculation errors across the GIS project, but the changes are reversible by resetting variables.

From the tool's definition The tool 'set_project_variable' 'Set a project-level variable' creates or modifies project configuration data that persists and is referenced by expressions throughout the QGIS project (as '@key').

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

set_project_variable Rate-limited

set_project_variable 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": {
    "set_project_variable": {
      "limits": [
        {
          "counter": "set_project_variable_rate",
          "window": "minute",
          "max": 30,
          "scope": "grant"
        }
      ]
    }
  }
}

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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 set_project_variable

What does the set_project_variable tool do? +

Set a project-level variable. Variables are accessible in expressions as @key. 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 set_project_variable? +

Register the QGIS MCP server in PolicyLayer and add a rule for set_project_variable: 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 set_project_variable? +

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

Can I rate-limit set_project_variable? +

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

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

set_project_variable 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.