An annotation may contain all or part of the following elements depending on the word limit and the content of the sources you are examining:
Source: https://services.unimelb.edu.au/__data/assets/pdf_file/0010/706951/Writing-an-annotated-bibliography-100113.pdf
Information found in an annotation may include:
"Based on 20 years of study, William A. Smith, Professor of English at XYZ University...";
"...sets out to place John Turner in eighteenth century England and show the development of his philosophy in relation to contemporary social mores";
"Smith addresses himself to the scholar, albeit the concluding chapters on capital punishment will be clear to any informed layman";
"Turner gears his study more to the romantic aspects of the age than the scientific and rational developments";
"Here Turner departs drastically from A. F. Johnson (Two will not, New York, Riposte Press, 1964) who not only has developed the rational themes of the eighteenth century but is convinced the romantic elements at best are only a skein through the major prose and poetry";
(e.g., bibliography, glossary, index, survey instruments, testing devices, etc.).
Source: http://lib.skidmore.edu/library/index.php/li371-annotated-bib