Described herein are methods and compositions relating to anti-Chi3L1 antibodies, antibody reagents, and antigen-binding fragments thereof which display superior properties, e.g., high sensitivity, high specificity, high binding affinity, neutralization activity ex vivo and in vivo (e.g., blocks Chi3L1-induced MAPK and AKT signaling). Methods of treatment, e.g., of treating cancer, obesity, and/or asthma by administering the compounds described herein are also provided.