PRECIS (2009) was a tool with 10 domains to design clinical trials on a continuum of explanatory attitude (ideal situation) to more pragmatic attitude (usual care). It was cited over 300 times by the end of 2014, but had weaknesses such as no rating scale, problems with some domains, and lack of validation. This paper presents PRECIS-2, a validated, improved version of the tool, along with guidance on how to use it. PRECIS-2 is a validated tool with nine domains—eligibility criteria, recruitment, setting, organisation, flexibility (delivery), flexibility (adherence), follow-up, primary outcome, and primary analysis—scored from 1 (very explanatory) to 5 (very pragmatic). It helps trialists make design decisions consistent with the intended purpose of their trial. The tool is designed to help trialists make the purpose of their trial explicit and ensure that their design choices are concordant with their intended purpose. PRECIS-2 has been developed with the help of over 80 international trialists, clinicians, and policymakers. It includes three new domains (recruitment, setting, and organisation) and has a 5-point Likert scale for each domain. It is intended to be used at the design stage of a trial to help trialists make the purpose of their trial explicit and ensure that their design choices are concordant with their intended purpose. The paper describes the PRECIS-2 tool and provides guidance on how to use it. It also discusses the nine domains of PRECIS-2 and how to use them. The domains include eligibility criteria, recruitment, setting, organisation, flexibility (delivery), flexibility (adherence), follow-up, primary outcome, and primary analysis. Each domain is intended to help trialists think about the consequences of that design decision for the applicability of the results of their trial. The paper also discusses the importance of applicability in trial design. Applicability is the ability for a trial result to be applied or used in a particular situation. It is the outcome of the design choices that affect the ease with which the trial results can be applied to and by the usual community of users of the intervention in the settings in which the trial designers envisioned it being used. The paper concludes that PRECIS-2 is a valuable tool for trialists to use in designing trials that are fit for purpose. It provides guidance on how to use the tool and discusses the nine domains of PRECIS-2 and how to use them. The paper also discusses the importance of applicability in trial design and how it affects the results of the trial.PRECIS (2009) was a tool with 10 domains to design clinical trials on a continuum of explanatory attitude (ideal situation) to more pragmatic attitude (usual care). It was cited over 300 times by the end of 2014, but had weaknesses such as no rating scale, problems with some domains, and lack of validation. This paper presents PRECIS-2, a validated, improved version of the tool, along with guidance on how to use it. PRECIS-2 is a validated tool with nine domains—eligibility criteria, recruitment, setting, organisation, flexibility (delivery), flexibility (adherence), follow-up, primary outcome, and primary analysis—scored from 1 (very explanatory) to 5 (very pragmatic). It helps trialists make design decisions consistent with the intended purpose of their trial. The tool is designed to help trialists make the purpose of their trial explicit and ensure that their design choices are concordant with their intended purpose. PRECIS-2 has been developed with the help of over 80 international trialists, clinicians, and policymakers. It includes three new domains (recruitment, setting, and organisation) and has a 5-point Likert scale for each domain. It is intended to be used at the design stage of a trial to help trialists make the purpose of their trial explicit and ensure that their design choices are concordant with their intended purpose. The paper describes the PRECIS-2 tool and provides guidance on how to use it. It also discusses the nine domains of PRECIS-2 and how to use them. The domains include eligibility criteria, recruitment, setting, organisation, flexibility (delivery), flexibility (adherence), follow-up, primary outcome, and primary analysis. Each domain is intended to help trialists think about the consequences of that design decision for the applicability of the results of their trial. The paper also discusses the importance of applicability in trial design. Applicability is the ability for a trial result to be applied or used in a particular situation. It is the outcome of the design choices that affect the ease with which the trial results can be applied to and by the usual community of users of the intervention in the settings in which the trial designers envisioned it being used. The paper concludes that PRECIS-2 is a valuable tool for trialists to use in designing trials that are fit for purpose. It provides guidance on how to use the tool and discusses the nine domains of PRECIS-2 and how to use them. The paper also discusses the importance of applicability in trial design and how it affects the results of the trial.