Wearable robots require compact sensing interfaces to monitor the forces transmitted through attachment straps. This study aims to combine strap fastening and force measurement in a lightweight buckle, enabling the magnitude and direction of strap loading to be monitored at the attachment interface. The proposed buckle incorporates two capacitive sensing cells and a flexure structure that converts applied loads into measurable capacitance changes. Their combined responses provide dual-axis force sensing within the buckle body. The complete device measures $64\times 45\times 10\mathrm{mm}$ and weighs $34\mathrm{g}$, including its sensing and signal-processing electronics. Its force and angle ranges are 0–$200\mathrm{N}$ and $\pm 8°$, respectively. The average capacitance sensitivity was $1.33\mathrm{fF}/\mathrm{N}$, and the force linearity error was $6.96\%$ of full scale of output (FSO). Force root-mean-square error (RMSE) was $7.34\%$ of FSO without initial preload and $1.21$–$1.76\%$ of FSO with approximately $18\mathrm{N}$ preload in the respective tests. The validation angle RMSE was $1.67\%$ of FSO. Force hysteresis and repeatability were $8.88\%$ and $0.51\%$ of FSO, respectively. The force and angle FSO values were $200\mathrm{N}$ and $16°$. The estimated $-3\mathrm{dB}$ bandwidth was $2.7\mathrm{Hz}$. The proposed design provides a compact sensing interface for strap-based wearable robots.