AI agents call tail_file to retrieve information from MCP Filesystem Server without modifying anything — typically the context-gathering step in research, monitoring, and reporting workflows, before the agent takes action elsewhere.
This tool retrieves file content without modifying, deleting, or executing anything. It is a simple query operation that reads trailing lines from a file. The narrow scope (last N lines) and read-only nature make this a low-severity Read operation.
From the tool's definition Tool name 'tail_file' and description 'Read the last N lines of a text file' both indicate a read-only operation with no side effects.
Documented attack patterns abuse exactly the kind of access tail_file gives an agent:
PolicyLayer is an MCP gateway — it sits between your AI agents and MCP Filesystem Server, and nothing reaches the server without passing your rules. This is the rule we recommend for tail_file:
{
"version": "1",
"default": "deny",
"tools": {
"tail_file": {}
}
}tail_file is read-only, so it stays allowed — but everything else on the server is denied unless you say otherwise.
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Read the last N lines of a text file. It is categorised as a Read tool in the MCP Filesystem Server MCP Server, which means it retrieves data without modifying state.
Register the MCP Filesystem Server MCP server in PolicyLayer and add a rule for tail_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.
tail_file is a Read tool with low risk. Read-only tools are generally safe to allow by default.
Yes. Add a rate_limit block to the tail_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 tail_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.
tail_file is provided by the MCP Filesystem Server MCP server (safurrier/mcp-filesystem). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
Deterministic rules across all 21 MCP Filesystem Server tools. Per-identity grants. Full audit log. Live in minutes. Nothing to install.
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21 MCP Filesystem Server tools catalogued and risk-classified — across an index of 42,500+ MCP servers.