I recently built Blendy, a tool to preview CSS Background blend modes rapidly.
Notable features:
Change background color
Preview gradients on the image
Change the size of the image
Upload images from Unsplash or your computer
Copy code for a blend mode
Try it out here: https://blendy.ml
Demo Video: Youtube
I first thought of Blendy when I had a tough time choosing blend modes for a background image. Each time I changed the blend mode in my editor, saw it in the browser and repeated the process. This seemed more like firing shots in the dark. 
Solution😃 : A tool where you can see all blend modes at once in different sizes and colors. You can also use it to preview linear gradients on the image.
I look forward to hear your thoughts.