Create a new file or completely overwrite an existing file with new content.
AI agents use write_file to create or update resources in Search — usually the action step of a workflow, after the agent has gathered context. Every call changes real data in your Search environment.
The tool creates or modifies files, which is a reversible Write operation. It is not Destructive because the original file content could theoretically be recovered in many scenarios (depending on the filesystem and OS).
From the tool's definition Tool description explicitly states 'Create a new file or completely overwrite an existing file with new content.' This is a write operation that modifies the filesystem.
Documented attack patterns abuse exactly the kind of access write_file gives an agent:
PolicyLayer is an MCP gateway — it sits between your AI agents and Search, and nothing reaches the server without passing your rules. This is the rule we recommend for write_file:
{
"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.
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Create a new file or completely overwrite an existing file with new content. It is categorised as a Write tool in the Search MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.
Register the Search 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 Search. 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 Search MCP server (@agent-infra/mcp-server-search). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
Start from Search, add the rest of your stack, and see everything your agents can call. Then put policy on all of it.
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36 Search tools catalogued and risk-classified — across an index of 43,000+ MCP servers.