Rapid access to mitochondrial marker genes is essential for species identification and phylogenetics, but conventional barcoding or genome skimming remains time-consuming and resource-intensive. Public RNA-Seq archives, an underused source of mitochondrial transcripts, can be leveraged through an ultralight, fully web-accessible pipeline that retrieves and assembles the complete cytochrome c oxidase subunit I (COX1) gene. Seven public Acheta domesticus RNA-Seq datasets (SRR7692599–SRR7692605) were retrieved from the NCBI Sequence Read Archive. A targeted BLAST-based filtering approach was applied to extract COX1-related reads, which were then assembled using the CAP3 tool on Galaxy Europe. Assembly quality was assessed by ClustalW alignment and confirmed by BLAST validation against the NCBI nucleotide database. Between 180 and 214 COX1-related reads (mean 200.9 ± 11.8) were recovered per dataset. CAP3 produced complete or extended COX1 contigs (1,545–1,784 bp; up to 116.5% of the 1,531 bp coding length due to flanking UTR-like sequence). All seven assemblies showed 100% nucleotide identity to the reference after orientation correction. No off-target mitochondrial genes or nuclear mitochondrial pseudogenes (NUMTs) were detected in BLAST validation. The entire process was completed within one hour using freely available web tools. This streamlined pipeline enables fast and accurate recovery of mitochondrial genes from public transcriptomic resources and can be adapted for other highly expressed genes. It provides a cost-effective alternative to traditional molecular methods.