Including pedestrians in urban design is vital so that they prefer walking over motorized transport. Motorized mobility, which mainly involves automobiles, has conditioned urban design, pedestrian movement, sustainability, and urban resilience. Studies of walkability in cities have recently been conducted, and they can be classified into those that use a qualitative observer-perception-based approach and a second approach based on the measurement of observable variables. This work aims to develop a tool that allows for walkability in public spaces to be evaluated based on directly observing reality while considering both approaches: those related to perceiving the environment and physical reality. Walking is one of the main ways of moving around and achieving sustainable urban mobility. The conditions of public spaces are fundamental for people in their preference for moving around by walking. A literature review related to walkability revealed that previous works included a variety of viewpoints, scales, tools, variables, and approaches. This study included a developed tool by modeling a definition of working areas, processing walkability data, and determining the Walkability Index (WI). The reliability of the data observed from the walkability variables was verified, and the tool’s usefulness for urban planning was demonstrated. Pedestrian-centered urban design promotes cities’ sustainable mobility, sustainability, and resilience. People’s conduct reveals how the urban environment is perceived. The developed WI evaluates the existing reality and allows for its evolution to be monitored.