write_file

THE RISK

Medium Risk

Why write_file needs a policy

This tool creates or modifies file content in Obsidian notes, which is a reversible Write operation. While overwriting could lose data, the operation itself is not inherently destructive—the previous state could be recovered through version control or undo.

From the tool's definition Tool description states 'Write file content with different modes: overwrite (default), append, or prepend.

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

POLICY

How to control write_file

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

policy.json

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

write_file 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 Obsidian Local REST API MCP Server — 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 Obsidian Local REST API MCP Server tools

Destructive delete_item Delete a file or directory from the vault Write create_or_update_note Create or update a note with content and frontmatter. Performs upsert operation - creates Read find_related_notes Find notes related to a given note based on shared tags, links, or backlinks Read get_daily_note Get daily note for a specific date. Handles common daily note naming conventions and file Read get_metadata_keys Get all available frontmatter keys from notes Read get_metadata_values Get all unique values for a specific frontmatter key Read get_note Get a specific note with its content and metadata (legacy) Read get_recent_notes Get recently modified notes, ordered by modification time

All 13 Obsidian Local REST API MCP Server 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 write_file

What does the write_file tool do? +

Write file content with different modes: overwrite (default), append, or prepend. Handles both create and update operations. It is categorised as a Write tool in the Obsidian Local REST API MCP Server MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.

How do I enforce a policy on write_file? +

Register the Obsidian Local REST API MCP Server MCP server in PolicyLayer and add a rule for write_file: 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 Obsidian Local REST API MCP Server. Nothing to install.

What risk level is write_file? +

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

Can I rate-limit write_file? +

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

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

write_file is provided by the Obsidian Local REST API MCP Server MCP server (j-shelfwood/obsidian-local-rest-api-mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.

Enforce policy on every Obsidian Local REST API MCP Server tool call.

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

CHECK YOUR STACK →