This scientific opinion proposes toolboxes of welfare indicators, and their corresponding outcomes of consciousness, unconsciousness or death, for developing monitoring procedures at slaughterhouses for poultry stunned using electrical waterbaths and gas mixtures or slaughtered without stunning. For waterbath stunning, the opinion proposes a toolbox of indicators for assessing consciousness in poultry at two key stages of monitoring: (a) between the exit from the waterbath stunner and neck cutting and (b) during bleeding. For gas stunning, the opinion proposes a toolbox of indicators for assessing consciousness in poultry at two key stages of monitoring: (a) during shackling and (b) during bleeding. For slaughter without stunning, a toolbox is proposed for confirming death prior to entering scald tanks. Various activities—including a systematic literature review, an online survey and stakeholders‘ and hearing experts‘ meetings—were conducted to gather information about the specificity, sensitivity and feasibility of the indicators. On the basis of such information, a methodology was developed to select the most appropriate indicators to be used in the monitoring procedures. The frequency of checking differs according to the role of each person with responsibility for ensuring poultry welfare. The personnel will have to check all the birds and confirm that they are not conscious following stunning with electrical waterbaths or gas mixtures and that they are dead before entering scald tanks. For the animal welfare officer, a mathematical model for the sampling protocols is proposed, giving some allowance to set the sample size of birds that he/she needs to check at a given throughput rate (total number of birds slaughtered in the slaughterhouses) and threshold failure rate (number of potential failures—birds that are conscious after stunning). Finally, different risk factors and scenarios are proposed to define a =normal‘ or a =reinforced‘ monitoring protocol, according to the needs of the slaughterhouse.