Expo iOS Development MCP Server

Instructions

Implementation Reference

• src/mcp/server.ts:598-622 (registration)

  Registers the ui.press_key MCP tool, providing description, input schema, and the handler function that generates a Detox snippet and executes it via runDetoxAction.

  server.tool(
    "ui.press_key",
    "Press a special key (return, backspace, delete)",
    UiPressKeyInputSchema.shape,
    async (args) => {
      try {
        const snippet = generatePressKeySnippet(args.key);
        const result = await runDetoxAction({
          actionName: `pressKey:${args.key}`,
          actionSnippet: snippet,
        });
        return {
          content: [
            {
              type: "text",
              text: JSON.stringify(result, null, 2),
            },
          ],
          isError: !result.success,
        };
      } catch (error) {
        return handleToolError(error);
      }
    }
  );

• src/mcp/server.ts:602-621 (handler)

  The core handler function for ui.press_key: generates Detox code snippet using the provided key and runs it, returning the result or error.

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

• src/mcp/schemas.ts:82-84 (schema)

  Zod schema defining the input for ui.press_key: requires a 'key' enum of supported special keys.

  export const UiPressKeyInputSchema = z.object({
    key: z.enum(["return", "backspace", "delete"]).describe("Key to press."),
  });

• src/detox/actions.ts:92-104 (helper)

  Helper function that generates the specific Detox test code snippet for pressing the given key (targets first UITextField).

  export function generatePressKeySnippet(key: KeyType): string {
    switch (key) {
      case "return":
        return `await element(by.type('UITextField')).atIndex(0).tapReturnKey();`;
      case "backspace":
        return `await element(by.type('UITextField')).atIndex(0).tapBackspaceKey();`;
      case "delete":
        // Delete key is same as backspace on iOS
        return `await element(by.type('UITextField')).atIndex(0).tapBackspaceKey();`;
      default:
        throw new Error(`Unsupported key: ${key}`);
    }
  }