add_table_join · QGIS MCP: Risk & Policy

WHAT IT DOES

What add_table_join does on QGIS MCP

AI agents use add_table_join 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_table_join needs a policy

Adding a table join modifies the structure and relationships of a vector layer by linking it to an external table, but this is reversible (joins can be removed). It does not delete data, execute arbitrary code, move money, or trigger uncontrolled external operations.

From the tool's definition Tool name 'add_table_join' combined with description 'Add a table join to a vector layer' indicates creation/modification of layer relationships and metadata. This is a write operation that modifies layer configuration.

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

add_table_join Rate-limited

add_table_join 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_table_join": {
      "limits": [
        {
          "counter": "add_table_join_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 add_table_join

What does the add_table_join tool do? +

Add a table join to a vector layer. 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_table_join? +

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

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

Can I rate-limit add_table_join? +

Yes. Add a rate_limit block to the add_table_join 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_table_join completely? +

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

add_table_join 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.