The J-Mini Plus is a portable laboratory-bench instrument used in the diamond trade to screen colourless gem-quality samples for type II diamond character and HPHT/CVD synthetic indicators. It is manufactured by HRD Antwerp, the Belgian gem laboratory associated with the Antwerp World Diamond Centre, and was introduced as a successor to the earlier J-Smart device.

The instrument operates by short-wave ultraviolet excitation and measurement of the resulting fluorescence and phosphorescence response, returning a referral or pass result for each tested stone. As with all such desktop screeners (the De Beers SYNTHdetect, the GIA iD100, the Yehuda Sherlock Holmes 2.0 and competing devices), the J-Mini Plus does not by itself determine that a stone is synthetic; it segregates a population of natural colourless diamonds from a referral group that includes most laboratory-grown diamonds and a smaller number of natural type II stones, which then require full laboratory analysis to resolve.

The device is positioned at the small-retailer and dealer-bench tier of the screening market and is widely used in the wholesale and parcel trade. Throughput, melee size range and reference-data updates are the principal points of comparison with competing instruments. As with all screeners, the operative limitation is that it tests one stone at a time or, in batch versions, in small populations, and that its reliability is dependent on the manufacturer's reference database being kept current as new synthetic-growth processes are introduced.