Copy file bytes (with optional line ranges) to agent's private buffer
AI agents use buffer_copy to create or update resources in Clippy — usually the action step of a workflow, after the agent has gathered context. Every call changes real data in your Clippy environment.
This tool reads file contents and writes them to an internal buffer, which is a reversible write operation. It doesn't execute code, delete data, or move money. Severity is medium because misuse could allow an AI agent to copy sensitive file contents to a buffer that might be accessible or leaked, but the operation itself is reversible and confined to a buffer rather than persistent storage or external systems.
From the tool's definition Tool description states it 'Copy file bytes...to agent's private buffer', which creates or modifies data in a buffer (Write operation). The tool name 'buffer_copy' and description indicate reversible data creation/modification.
Documented attack patterns abuse exactly the kind of access buffer_copy gives an agent:
PolicyLayer is an MCP gateway — it sits between your AI agents and Clippy, and nothing reaches the server without passing your rules. This is the rule we recommend for buffer_copy:
{
"version": "1",
"default": "deny",
"tools": {
"buffer_copy": {
"limits": [
{
"counter": "buffer_copy_rate",
"window": "minute",
"max": 30,
"scope": "grant"
}
]
}
}
}buffer_copy 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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Copy file bytes (with optional line ranges) to agent's private buffer. It is categorised as a Write tool in the Clippy MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.
Register the Clippy MCP server in PolicyLayer and add a rule for buffer_copy: 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 Clippy. Nothing to install.
buffer_copy 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 buffer_copy 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 buffer_copy. 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.
buffer_copy is provided by the Clippy MCP server (neilberkman/clippy). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
Start from Clippy, add the rest of your stack, and see everything your agents can call. Then put policy on all of it.
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7 Clippy tools catalogued and risk-classified — across an index of 43,000+ MCP servers.