write_file

Create a new file or completely overwrite an existing file with new content.

SERVERMCP Filesystem Server SOURCEa-niranjan/mcp-filesystem

Medium RISK CLASS

Category Write

Parameters 00 required

Recommended Rate-limitedsee the rule below

Registry record Grade F, identity unverified Pull the record →

This record as markdown: /tools/a-niranjan-mcp-filesystem/write-file.md

WHAT IT DOES

What write_file does on MCP Filesystem Server

AI agents use write_file to create or update resources in MCP Filesystem Server, usually the action step of a workflow, after the agent has gathered context. Every call changes real data in your MCP Filesystem Server environment.

RISK

Why write_file is rated Medium

This tool performs reversible data modification (create/overwrite files). It is not destructive because the overwritten data could theoretically be recovered from backups or version control, and the operation is not inherently irreversible like a delete operation.

From the tool's definition Tool description explicitly states: 'Create a new file or completely overwrite an existing file with new content.' The verb 'overwrite' combined with unrestricted file creation capability demonstrates write semantics.

Attacks that exploit this kind of access

RECOMMENDED RULE

The rule that runs write_file safely

PolicyLayer is an MCP gateway: it sits between your AI agents and MCP Filesystem Server, and checks every tool call against a rule you set before the call runs. Nothing changes on the server itself. For write_file, this is the rule to start with:

write_file Rate-limited

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.

View as policy code

policy.json

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

LIMIT THIS TOOL → Instant setup, no code required.

The button opens the PolicyLayer dashboard: create your workspace, connect MCP Filesystem Server, apply this rule, and every write_file call is checked against it from then on.

FAQ

Questions about write_file

What does the write_file tool do? +

Create a new file or completely overwrite an existing file with new content. It is categorised as a Write tool in the MCP Filesystem 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 MCP Filesystem 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 MCP Filesystem 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 MCP Filesystem Server MCP server (a-niranjan/mcp-filesystem). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.

KEEP EXPLORING

More on MCP Filesystem Server, and thousands of servers like it.

This server

All 17 MCP Filesystem Server tools →

Across the catalogue

write_file on 0sec → The MCP Attack Database →

Guides

Govern customer-ops agents →Argument validation →Scoped token →