A moderately large arboreal salamander, Bolitoglossa alvaradoi ranges in size from 106-155mm (total length), with a maximum recorded length of 159mm (6.25 inches). It has completely flat, webbed hands and feet, a prehensile tail, and large, protuberant eyes. Coloring within the species is highly variable, and individuals have been found to show coloration changes between the day and night. In general, B. alvaradoi has a uniformly black or dark brown venter and olive green to dark browm dorsum. The back may be marked with black spots, blotches, or a light middorsal patch of cream or tan coloration. At night, the darker ground color may lighten to gray, tan, or reddish brown with a pattern of scattered black or dark brown spots. Lightening of the dorsum may be so extreme that coloration patterns visible in the day are no longer discernible at night. Males and females may be distinguished by the number of costal grooves between adpressed limbs: males show only 1.5 to 2, females show 3 to 4. B. alvaradoi is similar to B. lignicolor but may be distinguished by the lack of light ventral spots and streaks, as is seen in the latter.(Leenders 2001; Savage 2002)
A Spanish-language species account can be found at the website of Instituto Nacional de Biodiversidad (INBio).