Connect Cursor to Plainrouter

Use Cursor Agent with Plainrouter over Streamable HTTP. You need Cursor with remote MCP support and an enabled Agent chat.

1. Try the sandbox

Merge this entry into your user-level ~/.cursor/mcp.json:

{
  "mcpServers": {
    "plainrouter-test": {
      "url": "https://plainrouter.com/mcp/sandbox"
    }
  }
}

Enable the server in Cursor’s MCP settings. The sandbox needs no Plainrouter account or key, returns synthetic data, and never contacts Meta. Ask:

Use plainrouter-test to call get_account_state, then get_signal_health.
Show the tool results and stop. Do not call other tools.

Both calls should succeed and include sandbox: true. This checks the connection, not production data or ad execution.

2. Create a workspace key

In Plainrouter, select your workspace and open Settings → Workspace keys. Create a Read key for analysis; use Write for Actions, including Actions record reads. Copy it once into your protected credential configuration. Each key covers one workspace. Never put keys in prompts or source control. Key permissions and replacement.

3. Add Plainrouter to the client

Add a separate production entry to the same mcpServers object:

{
  "plainrouter": {
    "url": "https://plainrouter.com/mcp",
    "headers": {
      "Authorization": "Bearer ${env:PLAINROUTER_WORKSPACE_KEY}"
    }
  }
}

Supply the variable to Cursor through your system environment or secret manager, then restart Cursor. This snippet is an entry inside mcpServers, not a replacement for the whole file.

4. Verify the connection

Start with this read-only request:

Use plainrouter to call get_install_instructions with no arguments.
Show the workspace and installation status, then stop. Do not change anything.

Check the tool result, not just the assistant’s summary: the workspace must be yours and the call must succeed. This workspace-only read works before connecting Meta. For account diagnostics, connect Meta and verify the selected account. Agent replies can vary. In Ask, changes wait for approval; in Full, policy-allowed changes run automatically. Rule violations are blocked in either mode. A client’s tool confirmation is separate from Plainrouter’s execution controls.

5. Troubleshooting

401 on tool calls: confirm Cursor inherited the key environment variable. A terminal variable does not necessarily reach an already-running desktop app.
Invalid config: preserve the outer mcpServers object and existing entries.
Tools are unavailable: check that the server and tools are enabled. Remote servers do not support envFile; use ${env:…} interpolation.

Reference: Cursor MCP configuration and environment variables. Choose another client.

Overview

Clients

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Reference

Connect Cursor to Plainrouter

1. Try the sandbox

2. Create a workspace key

3. Add Plainrouter to the client

4. Verify the connection

5. Troubleshooting

​1. Try the sandbox

​2. Create a workspace key

​3. Add Plainrouter to the client

​4. Verify the connection

​5. Troubleshooting

1. Try the sandbox

2. Create a workspace key

3. Add Plainrouter to the client

4. Verify the connection

5. Troubleshooting