Identify how parsley is used in your dish: raw garnish, cooking, or salad ingredient to choose the best substitute accordingly.
For fresh herbs like cilantro and chervil, use equal amounts and add at the end to maintain texture and flavor.
Use ¾ the amount of basil when substituting; tear leaves by hand and add fresh at the end to avoid discoloration.
For dried parsley, use 1 teaspoon per tablespoon of fresh parsley, and rehydrate in warm water or broth for 5 minutes before adding.
Use half the amount of tarragon and add late to preserve its licorice flavor; avoid in tomato-based or neutral dishes.
Taste and adjust as needed, especially with stronger herbs like cilantro, basil, and tarragon to prevent overpowering your dish.