Single nucleotide polymorphism (SNP) typing is crucial for drug dosage and disease progression. Therefore, a simple and convenient genotyping assay is essential for personalised medicine. Herein, we developed a non‐invasive, closed‐tube, and visualised method for genotyping. In this method, oral swabs were lysed to directly perform PCR coupled with nested invasive reaction and visualisation based on gold nanoparticle probes in a closed tube. The strategy for genotyping assay depends on the single base recognition property of invasive reaction. This assay allowed quick and simple sample preparation and the detection of 25 copies/μL of CYP2C19*2 and 100 copies/μL of CYP2C19*3 within 90 min. Further, 20 oral swab samples for CYP2C19*2 and CYP2C19*3 were correctly typed, which agreed with pyrosequencing, indicating that this method has great potential for SNP typing in source‐limited regions to guide personalised medicine.