Some seedlings are curvy and some aren't. But one might suspect that there isn't enough light, and this seedling is reaching for it. Sun for an hour or two a day won't do it.

You can try to salvage those if you wish. Transplant them deeply into fresh mix burying all that stretched weak stem. Bury them right up to just below the two cotyledons (leaves) and then find some way to get them 20x the amount of light they are getting now using supplemental lighting. Sunny windows never work.

Dave

Great idea Dave! Thanks! It never occurred to me to treat "newborn" seedlings this way. Makes sense!

Sunny windows aren't so bad. I don't know if it helps, but I remove the fly screens for more light, and I have more than one sunny window (one facing south and another facing west).

Linda

Sunny windows aren't useless. You can grow seedlings in them, and they'll do fine once you put them out. I used to do that routinely, long ago. But expect them to be leggy. Especially for tomatoes, that you can plant out deeply, leggy seedlings are doable. Now, that's with a few hours of sun. If you just get one or two, that's not enough.

Thank you for all the advice, I will tranplant them deeper into another container.

double pane windows generally block a lot of UV light, especially the more modern windows which are designed to block maximum UV. if located on south side, older single pane windows are the best for growing plants.

since tomatoes generally sprout and grow so fast, i would just seed another plant.. your call.

Interestingly, while fluorescents emit significant amounts of UV, particularly through cracks in the phosphors, LEDs for home illumination emit next to none. They work fine for growing plants. So I wouldn't worry too much about UV transmission of windows.