The “Jamdani” is more a weaving technique rather than a weave generic to a place. For the longest time it has been synonymous with Dhaka before the partition of Bengal. During the early 19th century due to the industrial revolution in England that brought in machine-made Jamdani, the actual Jamdani, woven on the looms, suffered a big setback and slowly started go extinct.
 A few designers took an interest and wanted to revive the traditional Jamdani. They trained the weavers on the weaving technique in the village of Uppada, Andhra Pradesh and made it popular with the name Uppada sarees and Neelambari in North India. More so in Uttar Pradesh and Varanasi


 The Jamdani is a supplementary weft technique of weaving, where the artistic motifs are produced by a non-structural weft, in addition to the standard weft that holds the warp threads together. The standard weft creates a fine, sheer fabric while the supplementary weft with thicker threads adds the intricate patterns to it. Each supplementary weft motif is added separately by hand by interlacing the weft threads into the warp with fine bamboo sticks using individual spools of thread. The result is a myriad of vibrant patterns that appear to float on a shimmering surface. What’s remarkable in this weaving technique is that the pattern is not sketched or outlined on the fabric. Instead, it is drawn on a graph paper and placed underneath the warp. Jamdani is a fine muslin cloth on which decorative motifs are woven on the loom, typically in grey and white. Often a mixture of cotton and gold thread were/was used.
To explain it in a more laymans parlance this is done using an extra weft in a grid manner looping in and out of the warp to form pattern.
The finer the base fabric, the more difficult, and greater skill done to do the Jamdani.
The difficulty level and intricacy depends on the fineness of the base fabric, the fineness of the extra weft- like zari, the no of colors etc.

I have attached here images of Jamdani on different fabrics including Tissue Benares, pure Zari Uppada which is extremely difficult just to give an idea and understanding. 
In my eyes even today think that the Uppadas of yore are the finest of Jamdani as far as closeness of weave is concerned. Still need a looking glass to see the looping!!

Silk Linen Jamdani - the inside of the saree is as fine as the outside.

Tangail Jamdani - The inside of the saree. Check if the base fabric is a looser weave, then the jamdani is easier.

The Chauranga Jamdani of Dhaka- Even though here the base fabric is of a loose weave- it is extremely difficult beacuse of the 4 colors of extra weft- There is also the panchrangi and satrangi

Pure silver Zari tussar Jamdani- to weave so many round buttas is extremely difficult.

Pure zari Uppada : also a jamdani weave

A neelambari tissue benares jamdani although this is the cut Jamdani.Cut work jamdani is the less expensive version of the Jamdani variety. In cut work the pattern or looping of thread is made to run from selvedge to selvedge, letting it hang loose between two motifs and the extra-thread is then cut manually, giving the effect of Jamdani. This is half as laborious because picking and counting of the warp us not there at every motif. Once the extra threads are cut the transparency of the saree comes through. But one negative here is that the back of the saree is rough on your skin because of the cut edges.

Muslin Jamdani from Bengal- the looping is very easily visible in this.

Jamdani as a technique combines great skill, creativity and hardwork.