We present a fragment-based decomposition analysis tool (FB-REDA) for the reorganisation energy (lambda). This tool delivers insights on how to rationally design low-lambda organic semiconductors. The contribution of the fragment vibrational modes to the reorganization energy is exploited to identity the individual contributions of the molecular building blocks. The usefulness of the approach is demonstrated by offering three strategies to reduce the reorganization energy of a promising dopant-free hole transport material (TPA1PM, lambda = 213 meV). A reduction of nearly 50% (TPD3PM, lambda = 108 meV) is achieved. The proposed design principles are likely transferable to other organic semiconductors exploiting common molecular building blocks.