Agalychnis callidryas, the Red-Eyed Tree Frog, is a slender, colorful, medium-sized frog. Females measure up to 77 mm, and males to 59 mm (Savage 2002). This frog has leaf-green to dark green dorsal surfaces; dark blue, purple, or brownish flanks, with cream-colored or yellow vertical or diagonal bars; blue or orange upper arms; thighs that are blue or orange on the anterior, posterior, and ventral surfaces; orange hands and feet, except for the outermost digits on each; a white ventrum; and protuberant red eyes, with vertical pupils (Savage 2002; Leenders 2001; Duellman 2001). The back is sometimes marked with faint tranverse darker green lines (especially in individuals from Nicaragua or Costa Rica) or small white dots (Duellman 2001). The average number of bars on the flanks increases in populations from north to south, with a mean of 5.0 bars in Mexico and a mean of 9.0 bars in Panama (Duellman 2001). In some populations from the middle part of the range (Nicaragua and Costa Rica, on the Caribbean side), there is often a continuous, longitudinal yellowish stripe connecting the upper ends of the vertical bars and separating the blue flanks from the green dorsum (Duellman 2001).

The skin is smooth both dorsally and ventrally (Savage 2002). Agalychnis callidryas has a rounded head and a truncated snout when viewed from above (Duellman 2001). Eyes are large and directed sideways (Leenders 2001). When this frog closes its eyes, transparent lower eyelids marked with a network of gold are apparent (Leenders 2001). It has distinct tympana (Savage 2002). The body is slender and somewhat flattened (Leenders 2001). Fingers are short, about one-half webbed, and have moderately large discs (Duellman 2001). The toes are short, about two-thirds webbed, and also have moderately large discs that are nearly as large as those on the fingers, with a narrow fold running from the heel to the disc of the fifth toe (Duellman 2001; Savage 2002). Adult males have paired vocal slits and a single internal median subgular vocal sac, as well as a grayish brown spinose nuptial pad at the base of each thumb (Savage 2002).

Young froglets (at least from Panama) are able to change color; they are green by day and change to purplish or reddish brown at night (Pyburn 1963). In addition, young froglets have yellow rather than red eyes, and have lighter-colored flanks lacking whitish bars (Pyburn 1963). The red eye coloration appears first at the periphery of the eye at about two weeks post-metamorphosis, and over a period of several days spreads inward to make the iris wholly red (Starrett 1960).

Agalychnis callidryas tadpoles are large, with a robust body that can measure 48 mm in total length at stage 34 (Savage 2002). The tail and caudal fins are moderately sized, with the tail tip narrowing to a thin flagellum (Savage 2002). The spiracle is sinistral and lateroventral, while the vent is dextral (Savage 2002). Eyes and nostrils are dorsolateral (Savage 2002). The mouth is anteroventral, with a small and complete oral disk, serrated beaks, and two upper plus three lower rows of denticles (Savage 2002; Duellman 2001). The row of denticles just above the mouth has a small gap medially (Savage 2002). Labial papillae are present on the lower lip in one to three rows lateral and ventral to the mouth, and on the upper lip in one to two rows lateral to the mouth, but lacking directly above the mouth (Duellman 2001). The tadpole body is olive gray dorsally, shading into a bluish gray speckled with olive-brown on the sides and undersides (Duellman 2001). Larval caudal musculature is a light grayish brown while the caudal fins are transparent, but both are speckled with dark gray (Duellman 2001).
 

The diploid number of chromosomes is 26 for Agalychnis callidryas (Duellman and Cole 1965).

A Spanish-language species account can be found at the website of Instituto Nacional de Biodiversidad (INBio).