  Visualization onboarding supports users in reading, interpreting, and
extracting information from visual data representations. General-purpose
onboarding tools and libraries are applicable for explaining a wide range of
graphical user interfaces but cannot handle specific visualization
requirements. This paper describes a first step towards developing an
onboarding library called VisAhoi, which is easy to integrate, extend,
semi-automate, reuse, and customize. VisAhoi supports the creation of
onboarding elements for different visualization types and datasets. We
demonstrate how to extract and describe onboarding instructions using three
well-known high-level descriptive visualization grammars - Vega-Lite,
Plotly.js, and ECharts. We show the applicability of our library by performing
two usage scenarios that describe the integration of VisAhoi into a VA tool for
the analysis of high-throughput screening (HTS) data and, second, into a
Flourish template to provide an authoring tool for data journalists for a
treemap visualization. We provide a supplementary website that demonstrates the
applicability of VisAhoi to various visualizations, including a bar chart, a
horizon graph, a change matrix or heatmap, a scatterplot, and a treemap
visualization.
