The agent’s answer
The numbers are concrete, though Donovan flags that guidelines vary. His default ask when he requests a synopsis is one to two pages, and he treats three-plus pages as a cue to trim, because agents do not want too much material. He carves out exceptions for high fantasy that needs worldbuilding and context, and for very long books exceeding roughly 120K words, where a longer synopsis is reasonable; a standard 70 to 90K word book only needs one to two pages. Separately, he advises condensing the query letter blurb to two or three paragraphs, or even one for a shorter, less thematically complex book, while warning writers not to omit major plot points that would later confuse the agent reading the manuscript.