CRISPRdirect is a web-based tool for designing CRISPR/Cas guide RNAs (gRNAs) with reduced off-target effects. It allows users to select rational target sequences from an input sequence, ensuring minimal off-target cleavage. The tool searches genomic sequences for potential target sites, considering the 5'-NGG protospacer adjacent motif (PAM) and the specificity of the target sequence within the genome. The server supports multiple organisms, including human, mouse, rat, and others, and provides detailed information on target sequences, such as GC content, melting temperature, and presence of TTTT sequences that may cause pol III termination. CRISPRdirect evaluates off-target sites by analyzing the number of perfect matches for each target sequence, with columns indicating the number of hits for 20-mer and 12- or 8-mer seed sequences adjacent to the PAM. It also allows users to visualize mismatches and gaps in potential off-target sites. The tool offers results in tab-delimited text or JSON format, facilitating automated gRNA design. It also provides a graphical view of target sites, aiding in the selection of paired gRNAs for complex targets. Compared to other tools, CRISPRdirect is efficient in processing large input sequences and provides a user-friendly interface for genome-wide CRISPR/Cas applications. It incorporates genomic sequences of various organisms, including X.tropicalis instead of X.laevis, due to the latter's complex genome structure. The tool is useful for designing gRNAs for difficult targets, such as histone clusters and ribosomal proteins, by allowing users to manually investigate potential off-target sites. CRISPRdirect is a powerful resource for genome engineering, offering high specificity and efficiency in gRNA design.CRISPRdirect is a web-based tool for designing CRISPR/Cas guide RNAs (gRNAs) with reduced off-target effects. It allows users to select rational target sequences from an input sequence, ensuring minimal off-target cleavage. The tool searches genomic sequences for potential target sites, considering the 5'-NGG protospacer adjacent motif (PAM) and the specificity of the target sequence within the genome. The server supports multiple organisms, including human, mouse, rat, and others, and provides detailed information on target sequences, such as GC content, melting temperature, and presence of TTTT sequences that may cause pol III termination. CRISPRdirect evaluates off-target sites by analyzing the number of perfect matches for each target sequence, with columns indicating the number of hits for 20-mer and 12- or 8-mer seed sequences adjacent to the PAM. It also allows users to visualize mismatches and gaps in potential off-target sites. The tool offers results in tab-delimited text or JSON format, facilitating automated gRNA design. It also provides a graphical view of target sites, aiding in the selection of paired gRNAs for complex targets. Compared to other tools, CRISPRdirect is efficient in processing large input sequences and provides a user-friendly interface for genome-wide CRISPR/Cas applications. It incorporates genomic sequences of various organisms, including X.tropicalis instead of X.laevis, due to the latter's complex genome structure. The tool is useful for designing gRNAs for difficult targets, such as histone clusters and ribosomal proteins, by allowing users to manually investigate potential off-target sites. CRISPRdirect is a powerful resource for genome engineering, offering high specificity and efficiency in gRNA design.