Bring a large pot of salted water to a rolling boil. Meanwhile, trim the asparagus to remove the white, fibrous ends. Cut asparagus into 2-inch pieces on the diagonal.
Add asparagus to boiling water and cook until bright green and just tender, 4 to 5 minutes. Drain asparagus in a colander and rinse with cold water until cool.
In a bowl, whisk together vinegar, mustard, parsley, tarragon, salt, pepper, onion powder, and garlic powder until blended. Add oil to vinegar mixture in a thin stream, whisking constantly. Season with additional salt and pepper.