Combine peaches, onion, vinegar, peppers, agave, jalapeno, garlic, cumin, and cayenne in a large pot. Bring to a boil and cook vigorously for 10 minutes, until the salsa no longer looks watery.
Funnel hot salsa into the prepared jars, leaving a 1/2 inch/12 mm of headspace. Wipe the rims, apply the lids and rings, and process in a hot water bath for 15 minutes.