set_custom_rule · Project Graph MCP: Risk & Policy

WHAT IT DOES

What set_custom_rule does on Project Graph

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

WHY IT NEEDS A POLICY

Why set_custom_rule needs a policy

This tool creates or modifies custom analysis rules within the project-graph system. While reversible (rules can be updated or deleted), it represents a Write operation that alters the system's analysis behavior and configuration state. It does not execute arbitrary code, delete irreversibly, or move money.

From the tool's definition Tool description states 'Add or update a custom code analysis rule. Creates ruleset if it does not exist.' — direct modification of stored rule configuration.

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

set_custom_rule Rate-limited

set_custom_rule 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_custom_rule": {
      "limits": [
        {
          "counter": "set_custom_rule_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 Project Graph, so you can run agents against it safely.

FAQ

Questions about set_custom_rule

What does the set_custom_rule tool do? +

Add or update a custom code analysis rule. Creates ruleset if it does not exist. It is categorised as a Write tool in the Project Graph 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_custom_rule? +

Register the Project Graph MCP server in PolicyLayer and add a rule for set_custom_rule: 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 Project Graph. Nothing to install.

What risk level is set_custom_rule? +

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

Can I rate-limit set_custom_rule? +

Yes. Add a rate_limit block to the set_custom_rule 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_custom_rule completely? +

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

set_custom_rule is provided by the Project Graph MCP server (rnd-pro/project-graph-mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.