My tomato plants have developed yellow spots on the leaves that are spreading quickly
That sounds rough yellow spots on tomato leaves that spread quickly usually point to disease or stress like overwatering or humidity affecting many plants at once
In my garden early blight showed up as yellow spots that spread fast I pruned infected leaves and improved airflow which slowed the spread
Could also be a magnesium deficiency or another nutrient issue but the fast spread makes disease more likely so keep checking for pattern and veins
Next steps water at soil level remove infected leaves mulch to keep leaves dry and watch for more signs then consider a labeled fungicide if many plants affected