AI agents use write_full_buf to create or update resources in Nvim — usually the action step of a workflow, after the agent has gathered context. Every call changes real data in your Nvim environment.
This tool modifies file content in a Neovim buffer. While the description is empty, the naming convention and context strongly indicate it writes/overwrites buffer contents. This is a Write operation (reversible modification) rather than Destructive since buffer content can be undone via Neovim's undo functionality.
From the tool's definition Tool name is 'write_full_buf' which indicates writing to a buffer. The server description states it 'Enables AI assistants to control running Neovim sessions' and the sibling tools include operations like 'add_virtual_text', 'find_and_replace_buf', and…
Documented attack patterns abuse exactly the kind of access write_full_buf gives an agent:
PolicyLayer is an MCP gateway — it sits between your AI agents and Nvim, and nothing reaches the server without passing your rules. This is the rule we recommend for write_full_buf:
{
"version": "1",
"default": "deny",
"tools": {
"write_full_buf": {
"limits": [
{
"counter": "write_full_buf_rate",
"window": "minute",
"max": 30,
"scope": "grant"
}
]
}
}
}write_full_buf 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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write_full_buf. It is categorised as a Write tool in the Nvim MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.
Register the Nvim MCP server in PolicyLayer and add a rule for write_full_buf: 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 Nvim. Nothing to install.
write_full_buf 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 write_full_buf 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 write_full_buf. 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.
write_full_buf is provided by the Nvim MCP server (paulburgess1357/nvim-mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
Deterministic rules across all 17 Nvim tools. Per-identity grants. Full audit log. Live in minutes. Nothing to install.
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17 Nvim tools catalogued and risk-classified — across an index of 42,500+ MCP servers.