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 manifestOACP.md- a plain-language context file for the app- an exported
.oacpContentProviderthat 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
Piece | Purpose |
|---|---|
| Declares capabilities, parameters, metadata, and invocation details. |
| Adds semantic context and disambiguation notes in plain language. |
| Serves |
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.
How OACP compares
OACP | Google Assistant Actions | Android 15 AppFunctions | Siri Intents | |
|---|---|---|---|---|
Min Android | 5.0 (API 21) | varies | 15 (API 35) | N/A (iOS) |
Open protocol | Yes (Apache 2.0) | No | No | No |
Assistant-agnostic | Yes | Google only | Google only | Apple only |
Discovery | ContentProvider | Play Console | System API | Info.plist |
Metadata richness | High (aliases, examples, hints, entities) | Medium | Low | Medium |
On-device only | Yes | No (cloud) | Yes | Partial |
Entity providers | Yes | No | No | Yes (via Shortcuts) |
OACP and AppFunctions may converge. We are exploring an annotation processor that generates both oacp.json and AppFunctions metadata from a single source.
Who is using it
Eight apps support OACP today, with more coming. See the ecosystem for the full list.
Start building
If you want to see OACP working, start with Try It Out. If you want to add OACP to your app, jump to Add OACP to Your App. For the full integration reference, see the Integration Guide.