Getting Started

Manual Setup

Step-by-step config for Cursor, Claude Desktop, and Claude Code.

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Requires Node.js 18+ — see Prerequisites if you need to install it.

Get Your API Key

1

Open Settings

Click your profile in the top-left of app.smallest.ai and select Settings.

Atoms platform profile dropdown showing the Settings option in the left sidebar
Open the settings menu from your profile dropdown
2

Go to API Keys

Click API Keys in the left sidebar, then click Create API Key in the top-right.

Atoms platform API Keys settings page showing existing keys and the Create API Key button
The API Keys page — click Create API Key to generate a new key
3

Name and Create

Give your key a descriptive name (e.g., smallest-mcp) and click Create API Key. Copy and save it — you won’t see it again.

Create New API Key dialog with a name input field and Create API Key button
Enter a name for your API key and click Create

Install

Open (or create) your Cursor MCP config file:

OSPath
Mac / Linux~/.cursor/mcp.json
Windows%USERPROFILE%\.cursor\mcp.json

Paste this config. If you already have other MCP servers, just add the "smallest" entry inside "mcpServers".

1{
2  "mcpServers": {
3    "smallest": {
4      "command": "npx",
5      "args": ["-y", "@developer-smallestai/smallest-mcp-server"],
6      "env": {
7        "ATOMS_API_KEY": "sk_your_api_key_here"
8      }
9    }
10  }
11}

Replace sk_your_api_key_here with your actual API key.

Don’t share your API key or commit it to git.

Restart your editor

Cmd+Shift+P (Mac) or Ctrl+Shift+P (Windows) → Developer: Reload Window

Verify

Go to Cursor Settings → MCP. You should see smallest listed with a green dot.

Open a new chat (make sure you’re in Agent mode, not Ask mode) and type:

List all my agents

You should see your agents listed back. If you do — you’re done!

Troubleshooting

Node.js isn’t installed or isn’t in your PATH. See Prerequisites for installation instructions.

  • Make sure the mcp.json file is valid JSON (no trailing commas)
  • Verify the file is at ~/.cursor/mcp.json (not inside a project folder)
  • Reload the window: Cmd+Shift+P → Developer: Reload Window
  • Check that you copied the full key starting with sk_
  • Generate a new key from app.smallest.ai → Settings → API Keys

Next steps

Head to the Prompt Cookbook — it has copy-paste prompts for everything you can do.