Aim of the study:
The fidelity of an intervention can be defined as the degree to which a program implemented following the program model, i.e. the set of well-defined procedures for such intervention. This article aims to describe the steps taken to develop the assessment tool of fidelity to the original protocol of intervention for critical time intervention – task shifting (CTI-TS)

Subject or material and methods:
The development of an instrument to assess the fidelity includes some key stages, as definition of the intervention model, definition of the key components of the intervention, preparation of a preliminary scale, development of assessment sheets fidelity, development of a manual application of scale fidelity, training assessor fidelity and test the preliminary scale carrying out a pilot study

Results:
According the experts opinion, 18 key components of the intervention were defined. From these components, was built the fidelity scale which consists of 20 items, divided into three sections, each evaluating one of the types of fidelity: compliance, context and competence.

Discussion:
The CTI-TS had its fidelity assessment method developed in accordance with the recommendations in the current literature.

Conclusions:
The protocol compliance is essential for the results, whether positive or not, can be credited to the intervention itself.