A. Attrition rate of the approval process of the proposed chemical probes. B. Approved probes were categorized to show their differentiation from available chemical modulators (i) targets for which there are currently no high-quality probes available; (ii) targets for which the donated probe promises a significant (e.g. 10-fold) benefit in potency or selectivity; (iii) cases in which the new donated probe has similar potency/selectivity as currently available probes but an entirely different chemotype; (iv) best in class compound where none of the above points apply and where the benefit lies in the availability of the control compound and/or the data annotation.