Agriculture is undergoing profound transformation in response to the global challenges of food security, pollution and climate change. In particular, some farmers are exploring and tentatively applying new practices based on agroecological principles. However, depending on biological regulation, these practices have uncertain results. In order to choose and monitor their changes, farmers use various indicators. In our study, we examined these indicators as they were applied in the implementation of technical changes, with a view to determining their exact nature, partly unexplored by agronomists. We held six interviews, performed a retrospective analysis of a redesign project involving five farmers and four advisors, observed collective visits at long-term field experiments, and organized a design workshop with eight farmers. We then coded the verbatim transcript in order to characterize the functions and attributes of the indicators, using the principles of grounded theory. Our results show that indicators have 22 different functions regarding the farmers’ technical action, grouped into five categories. The most common functions are more learning-oriented than assessment-oriented, e.g., “adaptation-monitoring” with 92 out of the 260 statements on indicators identified, and “understanding-reinterpretation” with 107 out of 260 statements. The attributes of the indicators are predominantly visual (62 %), relative (63 %), and passive (75 %). In addition, we found that indicators used at a strategic decision level are specific, as they are mostly quantified, concern large time and spatial scales, and are essentially dynamic, that is, interpreted in as trends