• Bibliographies are lists of the resources used in the writing of a document (paper, essay, article, book, etc.). 
• Bibliographies usually list the resources without any added comments.
• Annotated bibliographies are list of resources that also include comments by the person who is compiling the bibliography.
• Annotations can be divided into 2 basic categories:
  • Summarizing / Describing: Sentences that briefly and accurately re-state what the article says. 
  • Evaluating / Analyzing: Sentences that provide your judgment about the accuracy of the information, the usefulness of the examples, the clarity of the writing and explanations, and the persuasiveness of the arguments.
• The length can vary from a single sentence to several paragraphs. Always follow your professor's guidelines for the specifics of the assignment. In general, it might be good to provide 1-2 sentences of summary and 1-2 sentences of evaluation and perhaps another sentence that states how you will incorporate this resource in your paper.

MLA annotated bibliography format

https://style.mla.org/ 

The MLA Style Center and the current edition of the MLA Handbook provide the following guidance for formatting an MLA annotated bibliography:

• Title your reference page as “Annotated Bibliography” or “Annotated List of Works Cited.”
• Place each annotation after its reference.
• Annotations should typically not exceed a single paragraph.
• Annotations should be indented one inch from the start of your citation.
• Double-space all text on the page.
• 1-inch margins around the page.

Sources in an annotated bibliography can be organized alphabetically by the first word in each reference (as with a normal Works Cited page), by publication date, or by subject.

For a visual example of an annotated bibliography, as well as specific annotation examples, visit the MLA annotated bibliography guide.