A key lets another program work with your account: make events, add people, send, nudge, send updates, and read who is coming. It works over a REST API and over MCP, for assistants that speak it.
Make one in Settings, under Keys: Manage keys, then New key. Name it for what it's for, and copy the key when it's shown, because that is the only time you will see it. Lose it and you make another.
Revoke, beside a key, stops anything using it at once. It can't be undone.
A key follows the same rules you do. Nudges are capped, people who opted out aren't messaged, and creating an event or adding a guest sends nothing until the program calls send. Paying happens in the app, not through a key.
Any account can make keys; there is no charge for them. The reference, with every call and the MCP tools, is at simpleinvite.app/developers.