write_json_file · Claude File Management Server MCP

WHAT IT DOES

What write_json_file does on Claude File Management Server

AI agents use write_json_file to create or update resources in Claude File Management Server — usually the action step of a workflow, after the agent has gathered context. Every call changes real data in your Claude File Management Server environment.

WHY IT NEEDS A POLICY

Why write_json_file needs a policy

This tool creates or modifies files in a reversible manner (files can be edited or deleted later). While it can overwrite existing files, the operation is not inherently destructive since files retain recoverable state in most systems and the tool itself lacks delete functionality.

From the tool's definition Tool name 'write_json_file' and description 'Write data to JSON file' indicate creating or modifying JSON file contents. The verb 'Write' is explicit in both the name and description.

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

write_json_file Rate-limited

write_json_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_json_file": {
      "limits": [
        {
          "counter": "write_json_file_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 Claude File Management Server, so you can run agents against it safely.

FAQ

Questions about write_json_file

What does the write_json_file tool do? +

Write data to JSON file. It is categorised as a Write tool in the Claude File Management 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_json_file? +

Register the Claude File Management Server MCP server in PolicyLayer and add a rule for write_json_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 Claude File Management Server. Nothing to install.

What risk level is write_json_file? +

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

Can I rate-limit write_json_file? +

Yes. Add a rate_limit block to the write_json_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_json_file completely? +

Set action: deny in the PolicyLayer policy for write_json_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_json_file? +

write_json_file is provided by the Claude File Management Server MCP server (vipin1000/mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.