Please see attached the main reference articles. STROBE and MOOSE are useful to assess risk of bias, and GRADE system to assess overall quality of evidence and strength of recommendations.
.As far as I understand, descriptive studies , although also "observational", are different from "observational studies". In summary, the first do not look for inference.
I agree with Dr. Tezal again . Descriptive and analytical studies are , in which researcher is supposed to observe and analyse what is happening naturally, he is not allowed to intervene .
Please go through the article (link), ''the methodological quality assessment tools for preclinical and clinical studies, systematic review and meta-analysis, and clinical practice guideline: a systematic review'' which listed all current evaluation scales required for Systematic Reviews.
Also have a look on Supplementary Appendix of the article.