What is OACP?

OACP is an open protocol for Android apps. An app can describe what it can do, and a compatible assistant can discover and invoke those capabilities.

Think of this as MCP but for mobile apps, hence Open App Capability Protocol.

What ships today

Today, OACP is built around standard Android pieces:

• oacp.json - the machine-readable capability manifest
• OACP.md - a plain-language context file for the app
• an exported .oacp ContentProvider that serves those files
• Android Intents for foreground and background invocation

The public protocol spec and Android SDK currently target Android apps, not a general cross-platform runtime.

Why it exists

On Android, app-to-assistant integrations are usually vendor-specific. OACP is an attempt to make that contract open and reusable:

• App developers describe capabilities once.
• Assistants discover those capabilities at runtime.
• Invocation stays inside normal Android primitives instead of a closed platform API.

The protocol is separate from any one assistant. Hark is the reference implementation, not the protocol itself.

What an OACP app exposes

Assistants discover the app through the ContentProvider, parse oacp.json, and use Android Intents to invoke the selected action.

Two invocation patterns

Foreground handoff

Use an Activity action when the app needs to open:

• open the camera
• show a screen
• start an editor

The assistant resolves the action, calls startActivity(), and the app takes over.

Background action with async result

Use a broadcast action when the app can do the work without opening UI:

• fetch the weather
• read a stored value
• perform a background task

The assistant sends a broadcast, the app does the work, and the app can return an async result on org.oacp.ACTION_RESULT.

Start building

If you want to add OACP to an app today, start with Getting Started. If you want to see the protocol in action first, read Hark Overview.