Home and self-sampling STI kits have become a convenient, private option. Kits from regulated providers - especially those where you mail a sample to an accredited laboratory - can be very accurate for infections like chlamydia, gonorrhoea, HIV and syphilis when used as directed.
Accuracy depends on three things: using an approved kit, collecting the sample properly (following the instructions exactly), and testing after the relevant window period so the infection has time to become detectable. Rapid self-test devices done entirely at home can be slightly less reliable than lab-processed samples.
Treat home kits as a screening step, not the final word. A positive, unclear or borderline result should be confirmed by a licensed doctor or sexual-health clinic, which can also arrange treatment and partner notification. If you have symptoms, it is usually better to be seen in person rather than relying on a home kit alone.