A method is presented for determining strain in a magnetoresistive random access memory (MRAM) structure. The method includes exposing long lines of the MRAM structure to monochromatic light to produce a diffraction pattern, measuring changes in interference fringe spacing in the diffraction pattern, determining the changes in the local strain in the MRAM structure from the measured changes in the interference fringe spacing, and assessing a performance of the MRAM structure from values of the changes in the local strain.