AI agents use append_text_file_contents to create or update resources in Mcp Text Editor — usually the action step of a workflow, after the agent has gathered context. Every call changes real data in your Mcp Text Editor environment.
Appending to a text file creates or modifies data reversibly, which is the definition of Write category. While the modification is persistent, it is not destructive (data is not deleted or overwritten entirely) and can be undone by removing the appended lines.
From the tool's definition Tool name 'append_text_file_contents' and description 'Append content to a text file' indicates the tool modifies file contents by adding data.
Documented attack patterns abuse exactly the kind of access append_text_file_contents gives an agent:
PolicyLayer is an MCP gateway — it sits between your AI agents and Mcp Text Editor, and nothing reaches the server without passing your rules. This is the rule we recommend for append_text_file_contents:
{
"version": "1",
"default": "deny",
"tools": {
"append_text_file_contents": {
"limits": [
{
"counter": "append_text_file_contents_rate",
"window": "minute",
"max": 30,
"scope": "grant"
}
]
}
}
}append_text_file_contents 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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Append content to a text file. It is categorised as a Write tool in the Mcp Text Editor MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.
Register the Mcp Text Editor MCP server in PolicyLayer and add a rule for append_text_file_contents: 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 Text Editor. Nothing to install.
append_text_file_contents 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 append_text_file_contents 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 append_text_file_contents. 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.
append_text_file_contents is provided by the Mcp Text Editor MCP server (tumf/mcp-text-editor). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
Deterministic rules across all 6 Mcp Text Editor tools. Per-identity grants. Full audit log. Live in minutes. Nothing to install.
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6 Mcp Text Editor tools catalogued and risk-classified — across an index of 42,500+ MCP servers.