append_content

THE RISK

Medium Risk

Why append_content needs a policy

This tool adds content to files (creating new ones or extending existing ones), which is a reversible write operation. It does not delete or overwrite data, so it falls under Write rather than Destructive. Medium severity because an AI agent could pollute or corrupt vault notes, but data is recoverable.

From the tool's definition Append content to a new or existing file in the vault

Documented attack patterns abuse exactly the kind of access append_content gives an agent:

POLICY

How to control append_content

PolicyLayer is an MCP gateway — it sits between your AI agents and MCP server for Obsidian, and nothing reaches the server without passing your rules. This is the rule we recommend for append_content:

policy.json

{
  "version": "1",
  "default": "deny",
  "tools": {
    "append_content": {
      "limits": [
        {
          "counter": "append_content_rate",
          "window": "minute",
          "max": 30,
          "scope": "grant"
        }
      ]
    }
  }
}

append_content 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.

Create a free account and register MCP server for Obsidian — nothing to install.
Add this policy — paste it, or build it visually.
Point your MCP client (Claude, Cursor, anything) at your gateway URL.

LIMIT THIS TOOL →

Free to start. No card required.

EXPLORE

Related tools and policies

More MCP server for Obsidian tools

Destructive delete_file Delete a file or directory from your vault. Write patch_content Insert content into an existing note relative to a heading, block reference, or frontmatte Read get_file_contents Return the content of a single file in your vault. Read list_files_in_dir Lists all files and directories in a specific Obsidian directory Read list_files_in_vault Lists all files and directories in the root directory of your Obsidian vault Read search Search for documents matching a specified text query across all files in the vault

All 7 MCP server for Obsidian tools →

Write tools on other servers

M-Team MCP Server download_torrent YouTube MCP Server generate_video_title Android Forensics ADB MCP Server combine_reports 0xarchive web3_signup

Go deeper

The MCP Attack Database → Documented attack patterns against MCP deployments — and the policies that stop them.
Argument validation → Checking tool call arguments against schema and policy before they run.
Scoped token → Per-person credentials that grant a defined subset of servers and tools.
Rate Limiting MCP Tool Calls: A Practical Guide →
MCP Security: Why Prompt Guardrails Aren't Enough →

FAQ

Questions about append_content

What does the append_content tool do? +

Append content to a new or existing file in the vault. It is categorised as a Write tool in the MCP server 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 append_content? +

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

What risk level is append_content? +

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

Can I rate-limit append_content? +

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

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

append_content is provided by the MCP server for Obsidian MCP server (markuspfundstein/mcp-obsidian). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.

Enforce policy on every MCP server for Obsidian tool call.

Start from MCP server for Obsidian, add the rest of your stack, and see everything your agents can call. Then put policy on all of it.

CHECK YOUR STACK →