Extract a named function or class from a JavaScript file by name, returning its full source and line range. Use list_js_functions first to confirm the name. Only works within allowed directories.
AI agents call get_js_function to retrieve information from FilesystemMCP without modifying anything — typically the context-gathering step in research, monitoring, and reporting workflows, before the agent takes action elsewhere.
This tool retrieves and reads source code from JavaScript files within allowed directories. It performs a query/extraction operation with no side effects, no code execution, and no data modification. The returned data is the function's source code and metadata (line range).
From the tool's definition Tool name 'get_js_function' and description 'Extract a named function or class from a JavaScript file by name, returning its full source and line range' indicates retrieval of code without modification or execution.
Attacks that exploit this kind of access
Extract a named function or class from a JavaScript file by name, returning its full source and line range. Use list_js_functions first to confirm the name. Only works within allowed directories. It is categorised as a Read tool in the FilesystemMCP MCP Server, which means it retrieves data without modifying state.
Register the Filesystem MCP server in PolicyLayer and add a rule for get_js_function: 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 FilesystemMCP. Nothing to install.
get_js_function 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 get_js_function 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 get_js_function. 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.
get_js_function is provided by the Filesystem MCP server (rijadalisic/filesystemmcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
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