Combine the tomatoes, thyme, rosemary, oil, and salt in the bowl of a 4- to 6-quart slow cooker. Cover and cook on high for 4 hours, or until the tomatoes are softened and slightly wrinkled.
Let cool completely. Divide the tomatoes, cooking juices, oil, and herbs among 4 or 6 resealable rubber-rimmed jars.
Store in the refrigerator for up to 2 weeks.