Once.
CURSOR / MCP / EXECUTION SAFETY

Add Once execution safety to Cursor through MCP.

Installation boundary: default MCP exposes eight developer assessment/setup tools and does not automatically protect sibling GitHub, Adobe or other connectors. Registered actions are opt-in; the proxy protects only reviewed/configured upstream boundaries. The default helper supports Node 20+; local SQLite proxy/actions require 24.15+. The original durable ledger is execution authority: replacement, reset or rollback may permit an effect again, even at the same path. UNKNOWN never grants permission to redispatch. Authoritative compatibility and continuity matrix.

Once gives Cursor access to tools for identifying consequential writes, explaining retry risk, planning protection, applying approved protection and verifying a configured Once connection.

Short answer: Add @once-agent/mcp to your Cursor project so coding-agent workflows can evaluate and protect external writes that may otherwise be repeated after an ambiguous outcome.

Why this matters

AI coding agents can create software that performs payments, refunds, bookings, orders, provisioning, deployments, messages and other externally visible writes.

If one of those operations succeeds but its response is lost, another execution can repeat the same real-world effect.

Add Once through MCP

npx -y @once-agent/mcp

Once is published as an npm MCP server and registered under io.github.stringsofthemind-oss/once.

Cursor project configuration

{
  "mcpServers": {
    "once": {
      "type": "stdio",
      "command": "npx",
      "args": ["-y", "@once-agent/mcp"]
    }
  }
}

The Once repository includes a ready-to-copy .cursor/mcp.json project configuration.

View the Cursor + Once MCP example on GitHub

What the Once MCP server exposes

Claim boundary: Once does not claim universal exactly-once execution. Safety depends on stable operation identity, durable Once state, the provider integration and sufficiently authoritative provider truth. When an outcome cannot be established safely, Once can preserve uncertainty instead of blindly repeating the action.

Add Once to Cursor

npx -y @once-agent/mcp

Run the retry simulation · MCP package · Cursor configuration