Open · Nexus MCP for Obsidian MCP: Risk & Policy

WHAT IT DOES

What Open does on Nexus MCP for Obsidian

AI agents invoke Open to trigger actions in Nexus MCP for Obsidian. What it does depends on the arguments the agent supplies, and its effects often reach beyond the immediate call — builds kicked off, notifications sent, workflows started.

WHY IT NEEDS A POLICY

Why Open needs a policy

Opening a file in an editor is not a pure read; it triggers an application-level action (launching or switching the Obsidian editor to display a file). This is an external operation with side effects on the application state, placing it in the Execute category rather than Read. Severity is medium because misuse could disrupt the user's workspace or expose sensitive vault content in the UI.

From the tool's definition "Open a file in the editor" — triggers an external UI/editor operation beyond simple data retrieval

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

Open Rate-limited

Open stays usable, but rate-capped — a runaway agent can't fire it dozens of times a minute. Everything else on the server is denied unless you say otherwise.

View as policy code

policy.json

{
  "version": "1",
  "default": "deny",
  "tools": {
    "Open": {
      "limits": [
        {
          "counter": "open_rate",
          "window": "minute",
          "max": 10,
          "scope": "grant"
        }
      ]
    }
  }
}

RATE-LIMIT THIS TOOL →

Instant setup, no code required.

PolicyLayer is an MCP gateway: every tool call is checked against your rule before it reaches Nexus MCP for Obsidian, so you can run agents against it safely.

FAQ

Questions about Open

What does the Open tool do? +

Open a file in the editor. It is categorised as a Execute tool in the Nexus MCP for Obsidian MCP Server, which means it can trigger actions or run processes. Use rate limits and argument validation.

How do I enforce a policy on Open? +

Register the Nexus MCP for Obsidian MCP server in PolicyLayer and add a rule for Open: 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 Nexus MCP for Obsidian. Nothing to install.

What risk level is Open? +

Open is a Execute tool with high risk. Execute tools should be rate-limited and have argument validation enabled.

Can I rate-limit Open? +

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

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

Open is provided by the Nexus MCP for Obsidian MCP server (profsynapse/nexus). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.