The protocol is the detailed plan for your systematic review.  It sets out your rationale and methodology, and should be developed right at the beginning. You can refine it as you go on. 

Publishing your protocol in either a register or a journal will help avoid duplication of reviews. It also:

• reduces the likelihood of bias
• promotes transparency of methods and processes 
• allows for peer review of the planned methods. See Cochrane Handbook, Part 2, Chapter 1.5 - Protocol development.

For more information on the importance of protocols:

• The PLoS Medicine Editors. (2011). Best practice in systematic reviews: The importance of protocols and registration. PLoS Medicine, 8(2), e1001009. doi:10.1371/journal.pmed.1001009
• Equator Network (2015, January 23). Planning a systematic review? Think protocols [Blog post].

TIP: It's also a good idea to check through protocol registers to see if another group of researchers has already registered a review on your topic. (See the Where ... box below).

The PRISMA website (Preferred Reporting Items for Systematic Reviews and Meta-Analysis) has a page on PRISMA-P (PRISMA for Systematic Review Protocols).

PRISMA-P was published in 2015 to facilitate the development and reporting of systematic review protocols. 

Resources on the PRISMA-P webpage include:

• a statement paper, published in the journal Systematic Reviews
• an elaboration and explanation paper, published in BMJ
• a checklist available as a PDF or as a Word doc.

Typically, your systematic review protocol should include:

• Your rationale and objectives, including your PICO or other framework
• Your eligibility criteria (inclusions and exclusions)
• Your choice of sources (databases and grey literature), and your search strategy
• How you will screen your records, and extract, manage, and analyse the data.

• PROSPERO - “an international database of prospectively registered systematic reviews in health and social care, welfare, public health, education, crime, justice, and international development, where there is a health related outcome” (from About PROSPERO).Once you register your protocol on PROSPERO, it will be available on open access through their database. 
  
  Find out more here:  Guidance notes for registering a systematic review protocol with PROSPERO (University of York Centre for Reviews and Dissemination).
  
  NOTE: According to the Prospero home page, it does not have the resources to accept protocols from students.
   
• Cochrane Library - includes protocols of Cochrane Reviews that are planned or in progress. 
   
• JBI EBP Database – search for protocols by using the Publication Types drop-down menu under the search box.
   
• Open Science Framework (OSF) - a free open source project management tool.  You can register all types of review protocols including scoping reviews. For instructions on how to submit, see Welcome to registrations.
   
• Figshare - A free open access repository for sharing academic research outputs. You can register all types of review protocols including scoping reviews, and you can upload files in any format.
   
• The International Database of Education Systematic Reviews (IDESR) - A database of published systematic reviews in education, and a clearinghouse for protocol registration of ongoing and planned systematic reviews. Accepts registrations of review protocols for all areas of education. For guidelines on submission, see Inclusion criteria for IDESR protocols.
   
• Many journals will publish protocols - check the journals in your field. Instructions for authors will often have guidelines for the level of detail expected in the protocols they publish.