This document describes some advanced features. Most users probably won't need these, but you may find them useful depending on your use case.
You can auto-load a raster by setting url to the url of your raster in your url params. For example, http://app.geotiff.io/sum?url=https://s3.amazonaws.com/geotiff.io/PuertoRicoTropicalFruit.tiff will start the app with the raster of Puerto Rico's tropical fruit loaded.
GeoTIFF.io decides how many pixels to sample across and down for each Leaflet grid cell based on the getResolution function. Currently, you can adjust this resolution by setting a URL param of resolution. For example, loading https://app.geotiff.io?resolution=128 will load the site with twice the previously highest possible resolution.