A cleanliness monitor, an evaluation system and a method. The cleanliness monitor may include: a first vacuum chamber, a second vacuum chamber, a molecule collector, a release unit, a mass spectrometer, a manipulator that may be configured to move the molecule collector from the first position to the second position, and an analyzer. The mass spectrometer may have a line of sight to an inner space of the second vacuum chamber. The mass spectrometer may be configured to monitor the inner space of the second vacuum chamber and to generate detection signals that are indicative of a content of the inner space of the second vacuum chamber. A first subset of the detection signals may be indicative of a presence of the at least subset of released organic molecules. The analyzer may be configured to determine, based on the detection signals, the cleanliness of at least one out of (a) the first vacuum chamber, and (b) a tested vacuum chamber. The tested vacuum chamber is fluidly coupled to the first vacuum chamber.