The present study derived a short form of the State-Trait Cheerfulness Inventory-Trait Version (STCI-T30) using an item response theory framework. Latent trait test-retest correlations and reliability across the latent continuum in the STCI-T30 remained high. Moreover, the STCI-T30 showed external validity with criterion variables (e.g., playfulness) and a short writing task completed by these participants was rated by unacquainted judges to infer the author's cheerfulness, seriousness, and bad-mood. Results suggested significant self-other and inter-judge agreement of cheerfulness, seriousness, and bad-mood and linguistic cues analysis suggested cheerfulness and bad-mood manifested through writing in tone, social processes, and affect.