Inter-operation with other clouds, External Clouds (ECs), enhances elasticity of a cloud. In situations where an EC shuts down for maintenance or other purposes, the cloud that borrows resources from the EC must provide alternate resources to its users, whereas it does not usually do so, leading to loss or unavailability of resources to these users. Our work concentrates on this problem which appears to be unsolved to the best of our knowledge. We develop a toolkit, coined ‘Cloud Inter-operation Toolkit (CIT)', to handle this particular scenario, in addition to providing a sound inter-operation and all resource provisioning activities in an easier and less tedious manner. Thus, CIT makes the cloud highly tolerant to the shutting down of ECs that have provided resources to the cloud's users, thereby guaranteeing a more reliable and trustworthy cloud. As our work is a solution to an untouched problem, two new evaluation parameters have been introduced to study its effectiveness - Clot Time and Degree of Fault Tolerance. There is a healthy tolerance to the shutting down of ECs and resource provisioning is uninterrupted to the maximum extent possible, as is evident from the results obtained by evaluating our work. Thus, the successful cloud inter-operation provided by CIT enhances elasticity and ensures a high Transaction Success Rate while keeping the Turnaround Time as low as possible. © 2017 Elsevier Ltd