The development and publication of a protocol prior to the review being carried out is a key feature of systematic reviews. Transparent and clear documentation of the intentions and methods of the review assist in reducing the impact of authorial bias and allow for peer review of the proposed methodology.
Popular systematic review protocol registries are:
WARNING: some journals require protocol registration prior to starting the review. PLoS journals, BMJ and BMJ Open, BioMed Central and BJOG all recommend in their instructions to authors that details of protocol registration be included in manuscripts of both systematic review protocols and their final review reports/articles.