Replace · Nexus MCP for Obsidian MCP: Risk & Policy

WHAT IT DOES

What Replace does on Nexus MCP for Obsidian

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

WHY IT NEEDS A POLICY

Why Replace needs a policy

This tool modifies note content reversibly—users can undo changes or restore previous versions through Obsidian's version history or manual recovery. It is not Destructive because deletions are scoped to note content (not permanent vault destruction) and can be recovered. The validation mechanism (checking line content before replacement) mitigates accidental overwrites, reducing risk.

From the tool's definition Tool description states it 'Replace or delete existing content in a note' with validation checks before changes. The word 'replace' indicates reversible modification, and 'delete' here refers to content deletion within a note (not file destruction).

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

Replace Rate-limited

Replace 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": {
    "Replace": {
      "limits": [
        {
          "counter": "replace_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 Nexus MCP for Obsidian, so you can run agents against it safely.

FAQ

Questions about Replace

What does the Replace tool do? +

Replace or delete existing content in a note. Validates that the content at the specified lines matches before making changes. If the content has moved, returns the new line numbers. It is categorised as a Write tool in the Nexus MCP for Obsidian MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.

How do I enforce a policy on Replace? +

Register the Nexus MCP for Obsidian MCP server in PolicyLayer and add a rule for Replace: 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 Replace? +

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

Can I rate-limit Replace? +

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

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

Replace 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.