None of the three patentability criteria is defined in the TRIPS Agreement. Therefore, it is in the WTO Member states' discretion to determine the novelty standard in their national laws. If you compare different jurisdictions, you will find that the US, for example, adopted a relatively soft standard for novelty, whereas others, such as the European Patent Office, have stricter novelty standards.

Generally, novelty means that information describing the invention must not have been available to the public prior to the original application date (priority date). If such information is available to the public before that date, it is considered as part of "prior art". The more information is taken into account as prior art, the less likely it is that the invention meets the novelty criteria.

In a nutshell, you as a legislator/patent examiner are free to develop your own strict novelty standard, which would treat more inventions as prior art in the public domain and would thus make it more difficult to obtain exclusive patent rights.