Append a single import (or require) statement after the last existing import in a JavaScript file. Idempotent — does nothing if the exact statement is already present. Use this instead of replace_js_imports when you only need to add one new dependency. Only works within allowed directories.
AI agents use add_js_import to create or update resources in FilesystemMCP — usually the action step of a workflow, after the agent has gathered context. Every call changes real data in your FilesystemMCP environment.
This is a Write operation: it creates or modifies file content (JavaScript imports) in a reversible manner. The modification is non-destructive since imports can be undone by editing or deleting the added line.
From the tool's definition Tool appends import statements to JavaScript files, modifying file content. Description states 'Append a single import (or require) statement' and 'modify data reversibly' applies—imports can be removed or edited.
Attacks that exploit this kind of access
Append a single import (or require) statement after the last existing import in a JavaScript file. Idempotent — does nothing if the exact statement is already present. Use this instead of replace_js_imports when you only need to add one new dependency. Only works within allowed directories. It is categorised as a Write tool in the FilesystemMCP MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.
Register the Filesystem MCP server in PolicyLayer and add a rule for add_js_import: 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.
add_js_import 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 add_js_import 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 add_js_import. 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.
add_js_import 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.
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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