The study presents ResFinder, a web-based tool for identifying acquired antimicrobial resistance genes in whole-genome sequencing (WGS) data. ResFinder uses BLAST to compare short sequence reads or pre-assembled genomes against a database of known resistance genes. The tool was evaluated on 1862 GenBank files and 23 de novo sequenced isolates, showing high accuracy in identifying resistance genes with 100% identity. When tested on 23 isolates of five bacterial species, ResFinder showed good agreement with phenotypic testing, except for two cases where resistance genes were not detected despite phenotypic resistance. ResFinder was also evaluated on 30 isolates, where it correctly identified resistance genes in 29 cases. The tool is available online at www.genomicepidemiology.org and will be continuously updated as new resistance genes are identified. ResFinder is a valuable tool for identifying antimicrobial resistance genes in bacteria, providing a convenient and efficient method for resistance gene identification in routine diagnostic laboratories. The tool is designed to be user-friendly and accessible to investigators with limited bioinformatics experience. ResFinder can be used to identify resistance genes in completely sequenced isolates and to search for new resistance genes. The study highlights the importance of identifying antimicrobial resistance genes for understanding resistance mechanisms and epidemiology. ResFinder is a significant advancement in the field of antimicrobial resistance research, providing a reliable and efficient method for identifying resistance genes in bacterial isolates. The tool is expected to play a key role in the future of antimicrobial resistance research and diagnostics.The study presents ResFinder, a web-based tool for identifying acquired antimicrobial resistance genes in whole-genome sequencing (WGS) data. ResFinder uses BLAST to compare short sequence reads or pre-assembled genomes against a database of known resistance genes. The tool was evaluated on 1862 GenBank files and 23 de novo sequenced isolates, showing high accuracy in identifying resistance genes with 100% identity. When tested on 23 isolates of five bacterial species, ResFinder showed good agreement with phenotypic testing, except for two cases where resistance genes were not detected despite phenotypic resistance. ResFinder was also evaluated on 30 isolates, where it correctly identified resistance genes in 29 cases. The tool is available online at www.genomicepidemiology.org and will be continuously updated as new resistance genes are identified. ResFinder is a valuable tool for identifying antimicrobial resistance genes in bacteria, providing a convenient and efficient method for resistance gene identification in routine diagnostic laboratories. The tool is designed to be user-friendly and accessible to investigators with limited bioinformatics experience. ResFinder can be used to identify resistance genes in completely sequenced isolates and to search for new resistance genes. The study highlights the importance of identifying antimicrobial resistance genes for understanding resistance mechanisms and epidemiology. ResFinder is a significant advancement in the field of antimicrobial resistance research, providing a reliable and efficient method for identifying resistance genes in bacterial isolates. The tool is expected to play a key role in the future of antimicrobial resistance research and diagnostics.