The availability of suitable chemical building blocks, or reagents, is a key factor that determines the degree of effort required to make a target molecule. If a reagent is not available and requires synthesizing, this increases the total number of synthetic steps in the route and may result in a less attractive synthetic target. This can impact most in compound collection enhancement activities or early lead identification (LI) where typically not enough information or data are available to commit to such long multistep syntheses. In lead optimization (LO) projects, having access to commonly used reagents may improve the efficiency of building structure-activity relationships (SARs) and structure-property relationships (SPRs) around a core scaffold. This paper describes the systematic enumeration of key heteroaromatic reagent classes and the subsequent analysis of the availability of these in a number of commonly used databases.