Create or overwrite a file. Use paths relative to ${WORKSPACE}. Read the file first before writing.
AI agents use file_write to create or update resources in Docker MCP Server — usually the action step of a workflow, after the agent has gathered context. Every call changes real data in your Docker MCP Server environment.
This tool creates or modifies files, which is a write operation with reversible effects. While it can overwrite existing files (which has destructive intent), the files are scoped to an isolated Docker workspace and the operation itself is technically reversible through subsequent writes.
From the tool's definition Tool name is 'file_write' and description explicitly states 'Create or overwrite a file'. The tool modifies data (file content) reversibly within a containerized workspace.
Documented attack patterns abuse exactly the kind of access file_write gives an agent:
PolicyLayer is an MCP gateway — it sits between your AI agents and Docker MCP Server, and nothing reaches the server without passing your rules. This is the rule we recommend for file_write:
{
"version": "1",
"default": "deny",
"tools": {
"file_write": {
"limits": [
{
"counter": "file_write_rate",
"window": "minute",
"max": 30,
"scope": "grant"
}
]
}
}
}file_write 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.
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Create or overwrite a file. Use paths relative to ${WORKSPACE}. Read the file first before writing. It is categorised as a Write tool in the Docker MCP Server MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.
Register the Docker MCP Server MCP server in PolicyLayer and add a rule for file_write: 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 Docker MCP Server. Nothing to install.
file_write 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 file_write 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 file_write. 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.
file_write is provided by the Docker MCP Server MCP server (kenforthewin/docker-mcp-server). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
Start from Docker MCP Server, add the rest of your stack, and see everything your agents can call. Then put policy on all of it.
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9 Docker MCP Server tools catalogued and risk-classified — across an index of 43,000+ MCP servers.