Read the last N lines from a file
AI agents call tailFile to retrieve information from Expo MCP 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 (the last N lines) without modifying, deleting, or executing anything. It is a simple data retrieval operation analogous to the Unix 'tail' command. The blast radius of misuse is minimal: an attacker could read sensitive files if they exist and are accessible, but cannot modify state or trigger external operations. Classified as Read with low severity.
From the tool's definition Tool name is 'tailFile' and description explicitly states 'Read the last N lines from a file' — a read-only operation that retrieves data without side effects.
Attacks that exploit this kind of access
Read the last N lines from a file. It is categorised as a Read tool in the Expo MCP Server MCP Server, which means it retrieves data without modifying state.
Register the Expo MCP Server MCP server in PolicyLayer and add a rule for tailFile: 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 Expo MCP Server. Nothing to install.
tailFile 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 tailFile 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 tailFile. 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.
tailFile is provided by the Expo MCP Server MCP server (mattlemmone/file-mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
Every MCP server has a record like this.
Type a name, get the same breakdown: verified identity, auth posture, risk grade, capabilities, recommended policy.
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