update_buffer

THE RISK

Medium Risk

Why update_buffer needs a policy

This tool modifies file/buffer content in the editor in a reversible manner (edits can be undone in Neovim). It does not delete data, execute arbitrary code, or cause financial impact. The 'medium' severity reflects that an AI agent misusing this could corrupt or overwrite user files, but the changes remain recoverable through Neovim's undo system or by reopening the unmodified source file.

From the tool's definition Tool name 'update_buffer' and description 'Update the content of a buffer in Neovim. Changes appear immediately in the editor.' indicate modification of editor content.

Documented attack patterns abuse exactly the kind of access update_buffer gives an agent:

POLICY

How to control update_buffer

PolicyLayer is an MCP gateway — it sits between your AI agents and Neovim MCP Server, and nothing reaches the server without passing your rules. This is the rule we recommend for update_buffer:

policy.json

{
  "version": "1",
  "default": "deny",
  "tools": {
    "update_buffer": {
      "limits": [
        {
          "counter": "update_buffer_rate",
          "window": "minute",
          "max": 30,
          "scope": "grant"
        }
      ]
    }
  }
}

update_buffer 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.

Create a free account and register Neovim MCP Server — nothing to install.
Add this policy — paste it, or build it visually.
Point your MCP client (Claude, Cursor, anything) at your gateway URL.

LIMIT THIS TOOL →

Free to start. No card required.

EXPLORE

Related tools and policies

More Neovim MCP Server tools

Write reload_all_buffers Check all open buffers and reload any that have changed on disk. Use this after editing fi Write reload_buffer Reload a buffer from disk. Use this after editing a file externally to refresh the buffer Write open_file Open a file in Neovim. Use this to open newly created files or existing files for editing. Read get_buffer_content Get the content of a specific buffer by path Read get_current_buffer Get the currently active buffer in Neovim Read list_nvim_buffers List all open buffers in Neovim instances running in the current directory

All 7 Neovim MCP Server tools →

Write tools on other servers

M-Team MCP Server download_torrent YouTube MCP Server generate_video_title Android Forensics ADB MCP Server combine_reports 0xarchive web3_signup

Go deeper

The MCP Attack Database → Documented attack patterns against MCP deployments — and the policies that stop them.
Argument validation → Checking tool call arguments against schema and policy before they run.
Scoped token → Per-person credentials that grant a defined subset of servers and tools.
Rate Limiting MCP Tool Calls: A Practical Guide →
MCP Security: Why Prompt Guardrails Aren't Enough →

FAQ

Questions about update_buffer

What does the update_buffer tool do? +

Update the content of a buffer in Neovim. Changes appear immediately in the editor. It is categorised as a Write tool in the Neovim MCP Server MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.

How do I enforce a policy on update_buffer? +

Register the Neovim MCP Server MCP server in PolicyLayer and add a rule for update_buffer: 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 Neovim MCP Server. Nothing to install.

What risk level is update_buffer? +

update_buffer is a Write tool with medium risk. Write tools should be rate-limited to prevent accidental bulk modifications.

Can I rate-limit update_buffer? +

Yes. Add a rate_limit block to the update_buffer 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.

How do I block update_buffer completely? +

Set action: deny in the PolicyLayer policy for update_buffer. 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.

What MCP server provides update_buffer? +

update_buffer is provided by the Neovim MCP Server MCP server (laktek/nvim-mcp-server). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.

Enforce policy on every Neovim MCP Server tool call.

Start from Neovim MCP Server, add the rest of your stack, and see everything your agents can call. Then put policy on all of it.

CHECK YOUR STACK →