It is unanimously accepted that the term wohltemperiert in the title of Bach’s Das wohltemperierte Klavier refers to a tuning that makes it possible to compose and perform music without restriction in all twelve major and minor keys; however, there are still divergent opinions about the tuning that Bach preferred for his composition.
One view is that so-called equal temperament was assumed, in which the octave is divded into twelve equal half-tones (the tuning which came to be generally accepted over the course of the 19th century). Other scholars dispute this, but do not agree among themselves about how the nuances of the inequality in tuning are to be divided among the individual major and minor keys.
This according to Valuable nuances of tuning for part I of J.S. Bach’s “Das wohl temperirte Clavier” by Mark Lindley (Berlin: Staatliches Institut für Musikforschung Preußischer Kulturbesitz, 2011), which is an open-access multimedia resource for students and performers of Bach’s work.
Below, Gustav Leonhardt’s interpretation.