This diagram doesn't totally match my Ayurvedic diagram (this one's Chinese I believe) but it's close!
For tongue diagnoses, only look at the front of the tongue, the part used for speech, not at the back of the throat. If you stick out your tongue, the part that is visible is used in tongue diagnoses, basically.
A pale tongue indicates anemia, depletion
A coated tongue indicates toxins. If the toxins are towards the back of the tongue, the toxins are mainly in the colon. Middle to front means small intestine and stomach. Whitish toxins indicate mucous/Kapha derangement. Yellowish indicates Pitta/Bile derangement, such as too much bile in the gallbladder, small intestine. Redish/yellowish is Pitta type heat/toxins. Dark brown or black is Vata type weakness/cold.
Teeth impressions means poor absorbtion mostly in small intestine and some undigested foods in the intestines.
Froth means bronchitis.
Thready spit means candida, mucous from pastuerized milk or overly acidic system.
A single line bisecting the tongue represents the emotions stored in th spinal column. If this line is crooked or jagged, chances are there is a spinal subluxion or scoliosis.
Jagged cracks indicate Vata derangment, usually diarrhea, inflamed intestines. Very common to have this when cleansing/detoxing.
Bright red spot at the middle/near front of the tongue indicates heart issues.
A very smooth tongue (there should be raised papillea), or cracks, swelling, tenderness, soreness, also means Vitamin B deficiencies, which needs to be addressed immediately. Whole raw milk is the best way to go, but if you don't have access to that, drink the protein shake with rice milk and extra egg yolks.