The existing options like MCP or A2A are quite involved and for simple apps that are already URL parameter driven, those options seem like overkill.

This led me to prototype the Agent Use Interface (AUI) spec.

The idea is simple: a lightweight, open spec that makes any app "agent-navigable." You drop an XML file at /agents/aui.xml that describes the URL-parameter-driven actions your app supports, like search, create, filter, etc. And that way any AI agent can read aui.xml, understand what's possible, and construct URLs on behalf of the user.

That's it. No SDK. No auth flow. No API keys. Just a catalog of what your app can do, written for LLMs to understand.

Is there something like this that already exists? Is the approach too simple to be useful?

If your app already supports Universal Links or is otherwise URL parameter driven you could probably add support for AUI in an afternoon.

See a working example: https://habittiles.app/agents/aui.xml