LTR_FINDER is an efficient web server for predicting full-length long terminal repeat (LTR) retrotransposons. It uses structural features of LTR elements to accurately identify their locations and structures in DNA sequences. The tool is designed to rapidly scan large-scale genomic sequences and is the first web server for ab initio LTR retrotransposon discovery. It is freely accessible at http://tlife.fudan.edu.cn/ltr_finder/. LTR retrotransposons are common in eukaryotic genomes, especially in plants, and play important roles in genome and gene evolution. However, efficient tools for identifying these elements are limited. LTR_FINDER addresses this by using rapid algorithms and a multi-refinement process to construct reliable LTRs and predict accurate element boundaries. It also detects important enzyme domains to improve prediction confidence. The tool accepts DNA sequences in FASTA or multi-FASTA format and allows users to paste sequences or upload files. It provides two types of output: full-output with detailed predictions and summary-output with simplified information. Diagrams are available to visualize element locations and are useful for analyzing overlapping elements. In an example application, LTR_FINDER was used on the yeast genome, accurately predicting 50 full-length LTR retrotransposons. The server processed the entire yeast genome (12 Mb) in 30 seconds with low memory usage, detecting 52 models and identifying all 50 target elements with high accuracy and specificity. LTR_FINDER identifies LTR elements in four main steps: selecting possible LTR pairs, finding signals in near-LTR regions, validating enzyme domains, and gathering information to report possible models at different confidence levels. The tool is the first web server dedicated to full-length LTR retrotransposon discovery and is applicable for rapid analysis of large genomes. Future improvements include user-friendly interfaces, enhanced graphic outputs, and modules for finding nested elements.LTR_FINDER is an efficient web server for predicting full-length long terminal repeat (LTR) retrotransposons. It uses structural features of LTR elements to accurately identify their locations and structures in DNA sequences. The tool is designed to rapidly scan large-scale genomic sequences and is the first web server for ab initio LTR retrotransposon discovery. It is freely accessible at http://tlife.fudan.edu.cn/ltr_finder/. LTR retrotransposons are common in eukaryotic genomes, especially in plants, and play important roles in genome and gene evolution. However, efficient tools for identifying these elements are limited. LTR_FINDER addresses this by using rapid algorithms and a multi-refinement process to construct reliable LTRs and predict accurate element boundaries. It also detects important enzyme domains to improve prediction confidence. The tool accepts DNA sequences in FASTA or multi-FASTA format and allows users to paste sequences or upload files. It provides two types of output: full-output with detailed predictions and summary-output with simplified information. Diagrams are available to visualize element locations and are useful for analyzing overlapping elements. In an example application, LTR_FINDER was used on the yeast genome, accurately predicting 50 full-length LTR retrotransposons. The server processed the entire yeast genome (12 Mb) in 30 seconds with low memory usage, detecting 52 models and identifying all 50 target elements with high accuracy and specificity. LTR_FINDER identifies LTR elements in four main steps: selecting possible LTR pairs, finding signals in near-LTR regions, validating enzyme domains, and gathering information to report possible models at different confidence levels. The tool is the first web server dedicated to full-length LTR retrotransposon discovery and is applicable for rapid analysis of large genomes. Future improvements include user-friendly interfaces, enhanced graphic outputs, and modules for finding nested elements.