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What an Allternit Plugin is

An Allternit Plugin is a package that adds your product to Allternit. It has up to three parts: Users connect your server, sign in to your service through OAuth, and then the model can call your tools. If a tool has a UI, Allternit shows it in the chat.

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Built on an open standard

The UI layer is the open MCP Apps standard (specification version 2026-01-26), an extension of the Model Context Protocol. Allternit’s host implements the standard bridge, so a View that only uses the standard does not depend on Allternit. It runs in any host that implements the same specification. Allternit adds a small set of optional extensions under the x-allternit/* prefix (saving an artifact, dispatching an agent, and so on). They are feature-detected: a View that uses them keeps working in other hosts, with those features turned off. See window.allternit extensions.
Views that use only the standard bridge run in Allternit without changes. Views written for another host’s globals run through a compatibility shim or a small port. See Porting from other hosts.

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How the pieces fit

  1. The model calls a tool on your server. The tool declares _meta.ui.resourceUri, which points at a ui:// resource.
  2. When the call completes, the host reads that resource from your server (resources/read). The content is HTML with the MIME type text/html;profile=mcp-app.
  3. The host loads the HTML into a sandboxed iframe served from a separate origin (the sandbox proxy), under a Content Security Policy built from the csp you declared.
  4. The host sends the tool arguments and result to the View. The View renders them.
  5. The View can call your server’s tools back through the host (tools/call) and can ask the host to open links, send a message, or change display mode.
The View never talks to your server directly and never receives the user’s OAuth token. The host makes those calls on the user’s behalf.

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What is available today

This documentation describes what exists in the Allternit code. Some pieces are complete; others are a preview or still planned.

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Where to go next

Quickstart

Build a server with one data tool, one render tool, and a ui:// View.

Build: MCP server

Tools, schemas, annotations, and server instructions.

Build: MCP App UI

Bridge messages, theming, CSP, and sandbox rules.

Submit & review

Domain verification, scan checks, and review.