Markly

Markly is a measurement and design-spec plugin/extension for Photoshop and Sketch. It is made for modern Web designers and app front-end developers. You can add specification marks simply by clicking-and-dragging. Coordinates, dimensions, distance, or fonts, no matter what or where you want.

• Super Easy and Fast - Without Markly, you have to spend time applying styles to each individual specification element. Even if you create a list of styles in your layer settings--styles which execute an intricate set of steps--you will soon find the design difficult to maintain.
• Highly Maintainable - The efficiently organized measurements data are saved in the metadata of your file, ensuring high maintainability and portability.
• Smart Measure - Mobile developers don't use pixels (px) as Web developers do. Markly can automatically convert those measurements based on differing screen densities.
• Update Automatically - If you create specifications directly on your layers, once you modify your design, you have to modify the marks one-by-one according to the changes. You don't have to do this with Markly. Markly will update your specs automatically when you modify your design in Photoshop or Sketch.