Combine tomato sauce, brown sugar, vinegar, chili powder, garlic powder, onion powder, and red pepper flakes in a small bowl or mason jar. Whisk until well blended.
Let the sauce sit at room temperature for at least 30 minutes to let the flavors meld.
Notes
If you are in a hurry, you can combine the ingredients in a small saucepan and bring it to a simmer over medium heat.
You can store chili sauce in an airtight jar in the refrigerator for a week or two, or freeze it for up to six months.