Slice tomatoes as uniformly as possible to a maximum of 1/4" thickness.
If using olive oil, herbs, and salt before dehydrating, put the tomatoes in a bowl, add the oil, herbs, and salt on top of the tomatoes, and toss gently to coat.
Spread the tomato slices on dehydrator sheets in a single layer.
Place the dehydrator trays in the dehydrator.
Set the dehydrator to 125°F or desired temperature, and dehydrate until dry but still pliable, usually 8–24 hours depending on thickness and humidity.
The tomatoes are done when they are dry but still pliable (not moist or sticky).
Oven Method (Alternative)
Instead of using dehydrator trays, place the tomato slices or wedges on baking sheets with parchment.
Set the oven to its lowest temperature and place the trays in the oven.
Bake until dehydrated, flipping half way through if desired, and check the tomatoes often to prevent burning.
Notes
Slice the tomatoes uniformly (about 1/4 inch thickness) so that they dry at the same rate.
Check during drying (especially in the oven to avoid burning).
Oven tip: flip halfway if desired for more uniform and faster drying.
Dry until pliable for regular sun-dried tomatoes, or dry longer for extended storage.
For traditional sun-drying instructions, see the information in the post.