Nedev.FileConverters.XlsxToHtml 0.1.0

Nedev.FileConverters.XlsxToHtml

A high-performance, zero-dependency library and CLI for converting Excel (.xlsx) files to HTML targeting .NET 8.0 (and the library also supports .NETStandard 2.1).

Features

• No third-party dependencies – only .NET Base Class Library.
• Streaming XML parsing for low memory usage.
• Inline CSS styles reflecting cell formatting (fonts, colors, number/date formats; bold, italic, underline, background colors).
• Advanced number formatting: percent, fractions, conditional sections, and custom format strings are interpreted when possible (including basic color codes, positive/negative sections, and hex color specifications).

Custom colors

A static helper is exposed for named color lookup. Call ColorHelper.AddOrUpdate("name", "#RRGGBB") before conversion to register additional mappings (e.g. "orchid").

Formulas

If a cell contains a formula (<f> element) the HTML <td> will receive a title attribute containing the formula prefixed with =; the displayed value normally remains the cached result.
A runtime option allows basic evaluation of formulas (arithmetic, cell refs, ranges, SUM, AVERAGE):

var writer = new HtmlWriter { EvaluateFormulas = true };

• Console utility for batch conversions.

Usage

Convert a workbook to HTML using the CLI:

dotnet run --project src/Nedev.FileConverters.XlsxToHtml.Cli -- input.xlsx output.html

Omitting the output path will dump the HTML to standard output, making it easy to pipe.

Conversion is streaming and efficient; the entire document is never loaded into a DOM.

Building & Testing

The library multi-targets .NET 8.0 and .NET Standard 2.1; the CLI and tests target .NET 8.0.

This project depends on the Nedev.FileConverters.Core NuGet package. The library implements IFileConverter and is decorated with [FileConverter("xlsx","html")], enabling automatic discovery by the core infrastructure. The CLI also consumes the static Converter.Convert entry point from the core package.

Use the core API like so:

using Nedev.FileConverters;
using var outStream = Converter.Convert(inStream, "xlsx", "html");

# build all projects (run from repo root)
dotnet build src/Nedev.FileConverters.XlsxToHtml.slnx

# run unit tests for the path-based solution
dotnet test src/Nedev.FileConverters.XlsxToHtml.slnx

Limitations

• Formulas are not evaluated by default; set HtmlWriter.EvaluateFormulas to true for simple expressions.
• Images/charts and complex features (merged cells, comments) are not supported yet.

This repository is structured under src/ following .NET best practices.