Expo iOS Development MCP Server

Instructions

Implementation Reference

• src/mcp/server.ts:538-566 (registration)

  Registration of the 'ui.scroll' MCP tool, including the inline handler function that generates a Detox scroll code snippet using generateScrollSnippet and executes it via runDetoxAction.

  server.tool(
    "ui.scroll",
    "Scroll within a scrollable element",
    UiScrollInputSchema.shape,
    async (args) => {
      try {
        const snippet = generateScrollSnippet({
          selector: args.selector,
          direction: args.direction,
          amount: args.amount,
        });
        const result = await runDetoxAction({
          actionName: `scroll:${args.direction}:${describeSelector(args.selector)}`,
          actionSnippet: snippet,
        });
        return {
          content: [
            {
              type: "text",
              text: JSON.stringify(result, null, 2),
            },
          ],
          isError: !result.success,
        };
      } catch (error) {
        return handleToolError(error);
      }
    }
  );

• src/mcp/server.ts:542-565 (handler)

  Handler function for 'ui.scroll' tool: validates input via schema, generates Detox scroll snippet, executes via runDetoxAction, returns result or error.

  async (args) => {
    try {
      const snippet = generateScrollSnippet({
        selector: args.selector,
        direction: args.direction,
        amount: args.amount,
      });
      const result = await runDetoxAction({
        actionName: `scroll:${args.direction}:${describeSelector(args.selector)}`,
        actionSnippet: snippet,
      });
      return {
        content: [
          {
            type: "text",
            text: JSON.stringify(result, null, 2),
          },
        ],
        isError: !result.success,
      };
    } catch (error) {
      return handleToolError(error);
    }
  }

• src/mcp/schemas.ts:70-74 (schema)

  Zod input schema for 'ui.scroll' tool defining selector, direction (up/down/left/right), and optional scroll amount (pixels).

  export const UiScrollInputSchema = z.object({
    selector: SelectorSchema.describe("Scrollable element selector."),
    direction: DirectionSchema.describe("Scroll direction."),
    amount: z.number().optional().default(200).describe("Scroll amount in pixels."),
  });

• src/detox/actions.ts:50-65 (helper)

  Helper function generateScrollSnippet that creates the Detox JavaScript code for scrolling a scrollable element by amount pixels in the specified direction from relative start position.

  export interface ScrollOptions {
    selector: Selector;
    direction: Direction;
    amount?: number;
    startPositionX?: number;
    startPositionY?: number;
  }
  
  export function generateScrollSnippet(options: ScrollOptions): string {
    const el = buildElementExpr(options.selector);
    const amount = options.amount ?? 200;
    const startX = options.startPositionX ?? 0.5;
    const startY = options.startPositionY ?? 0.5;
  
    return `await ${el}.scroll(${amount}, '${options.direction}', ${startX}, ${startY});`;
  }