AI agents use edit_file_at_line to create or update resources in MCP Filesystem Server — usually the action step of a workflow, after the agent has gathered context. Every call changes real data in your MCP Filesystem Server environment.
This tool modifies file content at specific line numbers, which is a reversible write operation. It does not delete data (would be Destructive) or execute arbitrary code (would be Execute). The high severity reflects that unintended file edits could corrupt important files, though the operation is reversible.
From the tool's definition Tool name 'edit_file_at_line' and sibling tool 'edit_file' indicate file modification capability. The context of a Filesystem Server with file manipulation tools confirms this is a write operation.
Documented attack patterns abuse exactly the kind of access edit_file_at_line 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 edit_file_at_line:
{
"version": "1",
"default": "deny",
"tools": {
"edit_file_at_line": {
"limits": [
{
"counter": "edit_file_at_line_rate",
"window": "minute",
"max": 30,
"scope": "grant"
}
]
}
}
}edit_file_at_line 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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edit_file_at_line. It is categorised as a Write tool in the MCP Filesystem Server MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.
Register the MCP Filesystem Server MCP server in PolicyLayer and add a rule for edit_file_at_line: 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.
edit_file_at_line 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 edit_file_at_line 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 edit_file_at_line. 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.
edit_file_at_line 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.
Free to start. No card required.
21 MCP Filesystem Server tools catalogued and risk-classified — across an index of 42,500+ MCP servers.