The Electron Beam Ion Source (EBIS), developed to breed CARIBU radioactive beams at ATLAS, is being tested off-line (see Figure 1). A unique property of the EBIS is a combination of short breeding times, high repetition rates and large acceptance. Overall, we have implemented many innovative features during the design and construction of the CARIBU EBIS when compared to the existing EBIS breeders. The off-line charge breeding tests are being performed with the help of a surface ionization source that produces singly-charged caesium ions. The main goal of the off-line commissioning is to demonstrate stable operation of the EBIS at a 10 Hz repetition rate and a breeding efficiency into a single charge state higher than 15%. These goals have been successfully achieved and exceeded. We have measured (20 ± 0.7)% breeding efficiency into the single charge state of 28+ caesium ions with a breeding time of 28 ms. In general, the current CARIBU EBIS operational parameters can provide charge breeding of any ions over the full mass range of periodic table with high efficiency, short breeding times and sufficiently low charge-to-mass ratio, 1/6.3 for the heaviest masses, for subsequent acceleration by the ATLAS facility.