MCP Servers

The Index 01 assistant calls tools through the Model Context Protocol. The built-in actions (notes, reminders, timers, calendar, messaging) are MCP servers inside the Pebble mobile app. You can add your own server over HTTP, and the assistant lists its tools and calls them when a recording asks for something they do.

The MCP client is in mcp/src/commonMain/kotlin/coredevices/mcp/client/ and the settings screens are in experimental/src/commonMain/kotlin/coredevices/ring/ui/screens/settings/mcp/ of github.com/coredevices/mobileapp.

Requirements

The server speaks MCP over HTTP with either the SSE transport or the Streamable HTTP transport. Pick the matching one when you add the server.
The URL is reachable from the phone. Use HTTPS unless the server is on the same local network as the phone.
Authentication, if any, is a single static Authorization header value. OAuth flows are not supported.
tools/list returns every tool in one page. The app does not follow nextCursor.
Prompts are optional. Only prompts without arguments are offered, and only the text of the first message of a prompt is used.
Servers are called by a cloud model. See Cloud LLM Only.

Adding a Server

In the Pebble mobile app:

Open the Index 01 settings and tap MCP & Tool Settings.
Open the MCP Servers tab and tap Add MCP Server.
Enter a Name. Letters, digits, - and _ only, up to 32 characters. The name identifies the server in the app and in tool names.
Enter the URL. The app connects as you type, shows the server's title under the field when the connection works, and shows the error when it does not. A server that cannot be reached can still be saved.
Choose SSE or Streamable to match the server's transport. SSE is the default.
Under Groups, pick the sandbox groups the server belongs to. See Sandbox Groups.
To authenticate, expand Authorization (optional) and enter the full header value, for example Bearer token123.
If the server offers prompts, expand Prompts and select the ones to include.
Tap Save.

Edit a server by tapping it in the list. Delete removes it from every group.

The Authorization Header

The value you enter is sent as the Authorization header on every request the app makes to the server, including the connection check in the dialog, as entered. Include the scheme, so Bearer <token> rather than the bare token. The app does not refresh or rotate it. Leave the field empty for a server without authentication.

Prompts and Instructions

The instructions string a server returns from initialize is added to the assistant's context whenever the server is in the active group. Prompts you select in the dialog are fetched with prompts/get and appended after the instructions. Use them for standing guidance on when and how to call the server's tools.

Caching

The app caches tools/list and prompts/list results. If the server declares listChanged for tools or prompts, the cache lasts one hour and is cleared when the server sends the corresponding notifications/*/list_changed notification. Otherwise it lasts five minutes.

Sandbox Groups

A sandbox group is a set of MCP servers and the model that runs them. The Groups tab in MCP & Tool Settings lists them. Every phone has a group named Default MCP Sandbox that runs the Index agent with the built-in actions; servers you add to it are available to a gesture routed to Index agent. You can also create your own groups and route a recording gesture to one by choosing MCP sandbox on the Ring Button screen.

Each group has a Model Type:

Model type	Behaviour
Index Agent	The default Index assistant. Understands notes and the built-in actions. Cannot be customised.
Default	Fast at intent recognition. Fine for most tool sets.
High Capability	Slower. Better with large numbers of tools and more complex tasks.

Deleting a group does not delete its servers; they can be added to other groups.

Cloud LLM Only

Remote MCP servers are always called by a cloud model. The Agent Model setting in the Index 01 settings applies to the Index agent, which is what runs the Default MCP Sandbox group and any group whose model type is Index Agent:

With Cloud LLM or Cloud LLM (with Local fallback), HTTP servers in the default group are available to the Index agent.
With Local LLM, HTTP servers in the default group are shown as disabled with the reason "Remote MCP servers need the Cloud LLM". The on-device model also does not support every built-in action.
The Local LLM options cannot be selected while the default group's model type is Default or High Capability. Changing the default group to one of those model types switches Agent Model back to Cloud LLM.

Groups with the Default or High Capability model type run in the cloud whatever Agent Model is set to, and a gesture can be routed to them under any setting. They need a signed-in Pebble account.