Charttoolbox
Free browser-based heatmap generator for CSV and Excel
About Charttoolbox
Charttoolbox is a free heatmap generator for people who work with spreadsheet data and want a clear visual without learning charting code. It targets business report writers, academic researchers and anyone doing exploratory data analysis who needs a quick heatmap from a CSV, Excel file or pasted table.
Users can upload CSV, XLSX or XLS files, or paste cells straight from an open spreadsheet. Numeric columns can be turned into a Pearson correlation matrix automatically, and the tool offers sequential, diverging and color-blind-friendly palettes with adjustable limits and midpoint. Heatmaps can be exported as PNG for reports or SVG for editable figures.
The main difference is privacy: files are parsed and drawn on the user's device, and the site states that spreadsheet contents are not uploaded or stored. No account or sign-up is required. The site also offers other chart types, including bar, line, scatter and histogram tools.
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