This study compares the journal coverage of Web of Science (WoS) and Scopus in terms of fields, countries, and languages, using Ulrich's extensive periodical directory as a reference. The results indicate that both databases have biases that favor Natural Sciences and Engineering, as well as Biomedical Research, at the expense of Social Sciences and Arts and Humanities. Additionally, English-language journals are overrepresented, while other languages are underrepresented. While both databases share these biases, their coverage differs significantly, leading to variations in bibliometric analysis results depending on the database used. The study highlights the importance of considering these biases when assessing scientific activities and suggests that alternative tools, such as field-specific or national citation indexes, may be more suitable for certain types of analyses.This study compares the journal coverage of Web of Science (WoS) and Scopus in terms of fields, countries, and languages, using Ulrich's extensive periodical directory as a reference. The results indicate that both databases have biases that favor Natural Sciences and Engineering, as well as Biomedical Research, at the expense of Social Sciences and Arts and Humanities. Additionally, English-language journals are overrepresented, while other languages are underrepresented. While both databases share these biases, their coverage differs significantly, leading to variations in bibliometric analysis results depending on the database used. The study highlights the importance of considering these biases when assessing scientific activities and suggests that alternative tools, such as field-specific or national citation indexes, may be more suitable for certain types of analyses.