SAC mountain and alpine touring scale uses letter, based on the French or German word(s) indicating the technical difficultness. Also after the easiest grade (L/F) there are – and + to provide further granularity.

Alpine tour to Allalinhorn, graded L
Allalinhorn normal route, graded L

Similarly as with hiking scale, the grade is technical difficultness, not how physically demanding the route is. For example the normal route to Gletscherhorn is graded L and it has ascent of over 2000 meters which cannot be considered light by any standards.

Second very important point to highlight is that the mountain and alpine touring scale does not start where hiking scale ends. The T5-6 can be same as WS/PD, in other words, T6 can be significantly more challenging than L.

GradeRockFirn and glaciersUIAA GradeExample Tours
L
leicht / facile (/light)
F
Easy walking terrain (scree, simple block ridge).Simple firn slopes, hardly any crevices.from I.Piz Tschierva , east ridge
Wildhorn , from the Wildhornhütte
Bishorn , from the Tracuithütte

WS
wenig schwierig / peu difficile (/little difficult)
PD
+
Mostly still walking terrain, increased surefootedness required, climbing areas clear and problem-free.Usually not very steep slopes, short, steep passages, few crevasses.from IIPiz Palü , normal route
Balmhorn , normal route
Weissmies , normal route

ZS
ziemlich schwierig / assez difficile (/quite difficult)
AD
+
Repeated securing necessary, longer and exposed climbing sections.Steeper slopes, occasionally securing a stand, many crevices, small bergschrund.from IIIPiz Bernina , Biancograt
Mönch , west ridge
Matterhorn , Hörnligrat

S
schwierig / difficile (/difficult)
D
+
Good sense of route and efficient rope handling required, long climbing sections, usually require a secure stand.Very steep slopes, mostly securing a stand necessary, many crevices, large bergschrund.from IVPiz Palü , east pillar of the east summit
Eiger , Mittelegigrat
Weisshorn , Schaligrat

SS
sehr schwierig / très difficile (/more difficult)
TD
+
In the difficult sections, it is necessary to secure the stand throughout, consistently demanding climbing.Persistent steep terrain, continuous stand securing.from VPiz Bernina , direct west face
Doldenhorn , east ridge
Dent Blanche , north ridge

AS
äusserst schwierig / extrêmement difficile (/very difficult)
ED
+
Wall climbs that require great commitment.Very steep and vertical places, require ice climbing.from VIEiger north face (Heckmair)
Matterhorn , Zmuttnase

EX
extrem schwierig / abominablement difficile (/extremely difficult)
ABO
+
Extremely steep, partly overhanging wall passages.Ice climbing in extreme directions.from VIIEiger north face (various routes in the western part of the wall)

The overall rating is based on the key point, the crux, but in case there are significant differences, then route can have the higher grade first, and description that it goes down (e.g. ZS+, ascent to the summit ridge WS)

There are also a set of additional criteria: (1) demanding orientation, (2) difficult protection, (3) unreliable rock, and (4) aborting the tour problematic. In case one of these is elevated, the grade is raised by 1/3 step (e.g. from WS+ to ZS-), in case of several are elevated, then by 2/3 steps (from S+ to SS).

Next up: Via ferrata ratings (K1-K6)