Developmental editing, aka structural editing, is "big picture" editing that evaluates the book as a whole: 

• Does this scene/part make sense, or is it even needed?

• Are there any questions that arise for the reader? I'll help you identify any confusing parts and suggest ways to clarify.  

• Structure: Does it make sense, or are there parts that might be better moved around? 

• Pace: Are there any parts that drag too much? 

• Narrative style, tense, etc.; anything else that contributes to the entirety of the book. 

Line editing is just that: a line-by-line edit that is stylistic in nature yet still retains the author's original voice. This edit looks at: 

• Consistency in tense, viewpoint, and more 

• Sentence structure, pace, and flow 

• Word choice 

• Repetition and overwriting 

Proofreading is the type of editing that most people know and understand well. It is the last stage before publication, after the manuscript has undergone other rounds of editing. Proofreading includes finding and correcting: 

• Mistakes in spelling, punctuation, grammar

• Layout issues like indentation, missing page numbers, and line spacing

• Consistency in font and heading styles 

I was previously Lead Researcher at Nomadic Matt, and I love scouring the web (and books!) to find allllll the information needed for a project. AI is notoriously bad at factual accuracy; a real human is needed here. Research and fact-checking could include: 

• Ensuring accuracy of place, historical events, or people mentioned 

• Fully going down the research rabbit hole on a given topic to provide depth