write_file
Create a new file or completely overwrite an existing file with new content. Use with caution as it will overwrite existing files without warning. Handles text content with proper encoding. Only works within allowed directories.
This record as markdown: /tools/filesystem/write-file.md
What write_file does on Filesystem
AI agents use write_file to create or update resources in Filesystem, usually the action step of a workflow, after the agent has gathered context. Every call changes real data in your Filesystem environment.
| Parameter | Type | Required | Description |
|---|---|---|---|
path | string | Yes | |
content | string | Yes |
Parameters from the server's own tool schema.
Why write_file is rated Medium
The tool creates new files or modifies existing ones reversibly (files can be recovered or re-edited). While it can overwrite data, files are not irreversibly deleted—they remain recoverable through backups or version control. This is Write rather than Destructive.
From the tool's definition Tool description states: 'Create a new file or completely overwrite an existing file with new content' and explicitly warns 'it will overwrite existing files without warning.'
Risk signalsAccepts file system path (path) · Accepts raw HTML/template content (content)
Attacks that exploit this kind of access
The rule that runs write_file safely
PolicyLayer is an MCP gateway: it sits between your AI agents and Filesystem, 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 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.
The button opens the PolicyLayer dashboard: create your workspace, connect Filesystem, apply this rule, and every write_file call is checked against it from then on.
Questions about write_file
Create a new file or completely overwrite an existing file with new content. Use with caution as it will overwrite existing files without warning. Handles text content with proper encoding. Only works within allowed directories. It is categorised as a Write tool in the Filesystem MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.
write_file accepts 2 parameters: path, content. Required: path, content. The full parameter table on this page comes from the server's own tool schema.
Register the Filesystem 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 Filesystem. Nothing to install.
write_file is a Write tool with medium risk. Write tools should be rate-limited to prevent accidental bulk modifications.
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.
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.
write_file is provided by the Filesystem MCP server (@modelcontextprotocol/server-filesystem). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
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