What causes yellow spots on tomato leaves that spread quickly?

[Ronald48]

My tomato plants have developed yellow spots on the leaves that are spreading quickly

[Zoey14]

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

[OliviaDM]

In my garden early blight showed up as yellow spots that spread fast I pruned infected leaves and improved airflow which slowed the spread

[Scott51]

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

[ChloeJ]

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