cap-mcp-apps

cap-mcp-apps

CDS plugin for CAP Node.js. It enriches @cap-js/mcp query tool results with an MCP App (UI5 Web Components table) when the host supports MCP Apps.

CAP loads it automatically. A consuming app only needs this package in dependencies. There is no server.js protocol override.

Install

npm add @cap-js/mcp cap-mcp-apps

From GitHub before it is published to npm:

{
  "dependencies": {
    "cap-mcp-apps": "github:aelghanam/mcp-apps"
  }
}

Annotate services with @mcp as usual. On cds watch / cds serve, CAP detects cds-plugin.js, merges this package's cds configuration, and loads the plugin.

The plugin contributes the annotation vocabulary in vocab/ through:

"cds": {
  "requires": {
    "cap-mcp-apps-vocab": {
      "model": "cap-mcp-apps/vocab"
    }
  }
}

Peer packages (@sap/cds, @cap-js/mcp, express) resolve from the consuming app. .npmrc sets omit=peer so a nested @sap/cds is not installed inside this package.

Configuration

Query-table enrichment is on by default. To keep the stock @cap-js/mcp adapter, set:

{
  "cds": {
    "mcp": {
      "apps": {
        "queryTable": false
      }
    }
  }
}

When queryTable is false, this plugin does not override protocols.mcp.impl.

Action buttons (@mcp.apps.Action)

Unbound service actions can be shown in the MCP App UI. The annotation shape is declared in vocab/index.cds (mcp.apps.Action / mcp.apps.Placement).

annotate MyService.ping with @mcp.apps.Action: {
  placement: #Toolbar,
  label: 'Ping'
};

annotate MyService.submitOrder with @mcp.apps.Action: {
  placement: #Row,
  label: 'Submit Order',
  entities: [Books, ListOfBooks]
};

Use type references [Books], not element expressions (Books). Parentheses are CXL paths resolved in the action scope and fail to compile for entity names.

Input forms are inferred from CDS parameters: no parameters calls immediately, scalars become inputs, structured or many parameters use a JSON textarea.

The App invokes the existing MCP call tool via app.callServerTool. After a successful action it re-runs the last query (structuredContent.queryArgs). A Refresh button in the header does the same.

Only actions the current MCP user may call (@requires / @restrict) are included.

Logging

const LOG = cds.log('cap-mcp-apps')

{
  "cds": {
    "log": {
      "[development]": {
        "levels": {
          "cap-mcp-apps": "debug"
        }
      }
    }
  }
}

Develop this plugin

src/ is the App UI. npm run build bundles it into assets/query-table.html, which the adapter serves at runtime. UI5 Web Components and esbuild are devDependencies of this package.

npm install
npm run build

Link it into a CAP app with "cap-mcp-apps": "file:../cap-mcp-apps", then run cds watch in that app.

License

PolyForm Small Business 1.0.0. Use is free for an individual, and for an organization with fewer than 100 people and under the license's revenue cap (1,000,000 USD in 2019 dollars, adjusted for inflation). Larger organizations are not covered and need a separate commercial license from the copyright holder.

The CDS annotation namespace stays mcp.apps (@mcp.apps.Action). That name is the annotation API, not the npm package name.