The linear stability of microtearing modes (MTMs) is investigated using a combination of analytical theory and gyrokinetic simulations with the gyrokinetic electromagnetic numerical experiment code. This study covers both the plasma core and pedestal regions, aiming to identify the dominant parameters affecting MTM growth rates and frequencies. Theoretical predictions and simulation results are found to be in qualitative agreement, although discrepancies appear in the collisionless limit due to factors such as the neglect of magnetic drift effects. A systematic parameter scan reveals strong dependences on collisionality, electron temperature gradients (ETGs), magnetic shear, and the Shafranov shift. Trapped particles play a dual role—destabilizing MTMs at intermediate collisionalities but reducing growth at higher values. In the pedestal, strong gradients and unfavorable magnetic geometry amplify MTM activity by nearly an order of magnitude compared to the core. While the ETG significantly increases the growth rate in the pedestal, the ion temperature gradient has only a weak stabilizing influence. These results improve the physical understanding of MTMs in realistic tokamak conditions and suggest pathways for stabilization relevant to both conventional and spherical devices.