Preparing annotations unnerves some writers because, unlike for references, there isn’t a precise formula that dictates the specific content for an annotation. However, once you understand the three types of annotation content and the general tone that your writing should have, you will discover that writing annotations for online references is nearly as straightforward as writing the references themselves. While the extra writing might initially seem like a nuisance, an annotated bibliography is really an opportunity for you to demonstrate all of the work and thought that you have invested in the paper.

General Guidelines

An annotation represents your brief summary or opinion of a source, written in complete sentences. Be succinct, but focus on achieving the objective of the annotation rather than a preconceived word count, unless your instructor sets a specific rule about length. Annotations achieve one or more of three key objectives: summarizing the source, assessing its quality or discussing its relevance to your research. Your instructor probably will tell you which goals you need to meet. The length of your annotation will depend on how many objectives you must fulfill. Cornell University recommends that an annotation be one paragraph that is roughly 150 words long. Alternatively, if you are meeting more than one objective in the annotation, the Online Writing Lab at Purdue University encourages you to give each objective its own paragraph that contains approximately 75 words. Try to limit each objective to about 75 words so that each complete annotation is roughly 75 to 225 words. If your instructor declines does not provide detailed guidance for the bibliography, play it safe and address all three objectives.


The Writing Center at the University of North Carolina Chapel Hill likens summary annotations to book reports. All you need to do in a summary is briefly explain what the source says and give relevant information about the author. For example, if your source was a U.S. senator’s online journal article about the merits of government funding for scientific research, you would state the topic of the article, describe the author’s examples of government-funded research that benefited the public, state her conclusion that investing in science is worthwhile, and note that the author served in the Senate.


An assessment of a source critiques the author, her argument and her writing. Give your educated opinion about the validity and academic value of the online article or web page. Cornell University explains that critical annotations “expose the author’s point of view, clarity and appropriateness of expression.” For example, an evaluation of the senator’s online article would address how well she expressed her thesis and evidence, and how successfully she supported her conclusion. You should also address the source’s academic authority, which might require you to identify the author’s sources or her expertise in the field. If the senator was an accomplished research scientist at an Ivy League school before entering the Senate, where she chaired the subcommittee on Science and Space -- which would give her unique insight into both scientific research and government appropriations for science -- she would be a very credible source on the topic of her article. A bibliography that contains thoughtful evaluative annotations can be one of your paper’s greatest assets. Critical annotations are your opportunity to demonstrate that you referenced some of the best scholarship in the field. Well-crafted assessments can help your grade.


When you reflect on a source’s relevance to your paper, consider two things: how much of your position or writing was influenced by the source and how valuable the source was when compared to your other sources. State any questions you had about the topic that the source answered. If it was weak compared with other sources that you referenced, say so. As long as you researched the paper well, it is perfectly acceptable to have sources that were less helpful or less meaningful than others. Annotations cannot be right or wrong as long as they are truthful and accurate.


MLA and APA styles format annotated bibliographies the same way, except for a few minor differences in page titling and spacing. The style guide you follow affects how you format the page and the online references, but it will not affect the content of the annotations. Because you will probably have to discuss the credibility of your sources in their respective annotations, take the extra time to identify the authors of your sources and the authors' credentials. This is easy to forget and occasionally hard to accomplish if you are referencing websites, which do not always identify authors or their credentials alongside the primary content. Though it might be time-consuming to abandon a reasonable source because it lacks thorough documentation or fails to establish the credibility of the author, trying to obscure a source’s weaknesses as you write an annotation will ultimately be more time-consuming, and it probably will harm your grade. It is fine to have sources that were less relevant that other references, but citing weak sources for which you cannot establish the author’s credibility is a costly mistake.