Introduction

Aspose.Cells FOSS for .NET is a free, MIT-licensed open-source library that enables .NET developers to create, load, edit, and save Excel .xlsx workbooks without any Microsoft Office installation or native COM dependency. It is distributed as the Aspose.Cells_FOSS NuGet package and runs on Windows, macOS, Linux, Docker, and serverless environments.

The library covers the full workbook lifecycle: constructing Workbook objects from scratch or from existing .xlsx files, navigating worksheets, reading and writing cell values of multiple data types, evaluating formulas, applying Style objects, setting up conditional formatting rules, adding data validations, managing hyperlinks and named ranges, and configuring page setup for print. All operations work against .xlsx files with no runtime dependency beyond the NuGet package itself.

Whether you are building a financial reporting API, a data export pipeline, or an automated test harness that validates spreadsheet output, Aspose.Cells FOSS for .NET provides a stable, audit-friendly foundation licensed for both open-source and commercial use.

Key Features

Workbook and Worksheet Management

Create workbooks from scratch or load existing .xlsx files using new Workbook() or new Workbook(filePath). Access worksheets by index or name via WorksheetCollection, add and rename sheets, set visibility, and save back to a file path or Stream with Workbook.Save(). Configure load-time repair with LoadOptions (TryRepairPackage, TryRepairXml) to handle malformed files gracefully.

using Aspose.Cells_FOSS;

var workbook = new Workbook();
var sheet = workbook.Worksheets[0];
sheet.Cells["A1"].PutValue("Hello");
sheet.Cells["B1"].PutValue(123);
sheet.Cells["C1"].Formula = "=B1*2";

workbook.Save("hello.xlsx");

var loaded = new Workbook("hello.xlsx");
Console.WriteLine(loaded.Worksheets[0].Cells["C1"].Formula);
Console.WriteLine(loaded.Worksheets[0].Cells["C1"].StringValue);

Cell Styling and Formatting

Apply Style objects to cells for font properties, fill color, borders, number formats, and alignment. Read the current style with Cell.GetStyle(), modify it, and commit with Cell.SetStyle(). The styling API uses FillPattern.Solid with ForegroundColor for background fills, and Style.Font.Bold for font weight control.

using Aspose.Cells_FOSS;

var workbook = new Workbook();
var cell = workbook.Worksheets[0].Cells["A1"];
cell.PutValue("Styled");

var style = cell.GetStyle();
style.Font.Bold = true;
style.Pattern = FillPattern.Solid;
style.ForegroundColor = Color.FromArgb(255, 241, 196, 15);
cell.SetStyle(style);

Console.WriteLine($"{cell.StringValue} / Bold={cell.GetStyle().Font.Bold}");

Conditional Formatting

Add conditional formatting rules to any cell range via ConditionalFormattingCollection. Supported rule types include FormatConditionType.CellValue, Expression, ColorScale, DataBar, and IconSet. Use OperatorType values such as Between, Equal, and GreaterThan to define conditions, then assign a Style to matched cells for visual highlighting.

using Aspose.Cells_FOSS;

var workbook = new Workbook();
var sheet = workbook.Worksheets[0];

var cfCollection = sheet.ConditionalFormattings[sheet.ConditionalFormattings.Add()];
cfCollection.AddArea(CellArea.CreateCellArea("A1", "A10"));
var rule = cfCollection[cfCollection.AddCondition(
    FormatConditionType.CellValue, OperatorType.Between, "3", "7")];
var style = rule.Style;
style.Pattern = FillPattern.Solid;
style.ForegroundColor = Color.FromArgb(255, 255, 199, 206);
style.Font.Bold = true;
rule.Style = style;

workbook.Save("conditional-formatting.xlsx");

Data Validation

Define list, decimal, and custom validation rules on any cell range using Worksheet.Validations. Each Validation instance supports ValidationType, OperatorType, formula bounds, input prompts, error messages, and ValidationAlertType for warning versus stop alerts. Validations survive a full save-load cycle.

using Aspose.Cells_FOSS;

var workbook = new Workbook();
var sheet = workbook.Worksheets[0];
sheet.Name = "Validation Sheet";

var listIdx = sheet.Validations.Add(CellArea.CreateCellArea("A1", "A3"));
var listVal = sheet.Validations[listIdx];
listVal.Type = ValidationType.List;
listVal.Formula1 = "\"Open,Closed\"";
listVal.IgnoreBlank = true;
listVal.InCellDropDown = true;
listVal.ShowInput = true;
listVal.InputTitle = "Status";
listVal.InputMessage = "Pick a status";

workbook.Save("validations-sample.xlsx");

Add external URLs, internal cell references, and mailto: links via HyperlinkCollection.Add(). Set Hyperlink.TextToDisplay and Hyperlink.ScreenTip for user-visible labels. Define workbook-scoped or sheet-scoped named ranges with DefinedNameCollection.Add() to create stable anchors for formulas and chart data sources.

using Aspose.Cells_FOSS;

var workbook = new Workbook();
var sheet = workbook.Worksheets[0];

sheet.Cells["A1"].PutValue("Docs");
var link = sheet.Hyperlinks[sheet.Hyperlinks.Add("A1", 1, 1, "https://example.com/docs")];
link.TextToDisplay = "Docs";
link.ScreenTip = "External documentation";

var name = workbook.DefinedNames[workbook.DefinedNames.Add("PrimaryRange", "='Sheet1'!$A$1:$D$5")];
name.Comment = "Primary data range";

workbook.Save("hyperlinks-names.xlsx");
Console.WriteLine("Hyperlinks: " + sheet.Hyperlinks.Count);
Console.WriteLine("Defined names: " + workbook.DefinedNames.Count);

Quick Start

Install the package:

dotnet add package Aspose.Cells_FOSS

Create a workbook, write mixed-type values and a formula, save to .xlsx, then reload and verify:

using Aspose.Cells_FOSS;

var outputPath = Path.Combine(AppContext.BaseDirectory, "cell-data-roundtrip.xlsx");
var timestamp = new DateTime(2024, 5, 6, 7, 8, 9, DateTimeKind.Utc);

var workbook = new Workbook();
var sheet = workbook.Worksheets[0];
sheet.Cells["A1"].PutValue("Hello");
sheet.Cells["B1"].PutValue(123);
sheet.Cells["C1"].PutValue(true);
sheet.Cells["D1"].PutValue(12.5m);
sheet.Cells["E1"].PutValue(timestamp);
sheet.Cells["F1"].PutValue(10);
sheet.Cells["G1"].PutValue(20);
sheet.Cells["G1"].Formula = "=F1*2";
workbook.Save(outputPath);

var loaded = new Workbook(outputPath);
var loadedSheet = loaded.Worksheets[0];
Console.WriteLine(loadedSheet.Cells["A1"].StringValue);
Console.WriteLine(loadedSheet.Cells["G1"].Formula + " -> " + loadedSheet.Cells["G1"].StringValue);

Supported Formats

FormatExtensionReadWrite
Xlsx.xlsx✓✓
Auto(various)✓—

Open Source & Licensing

Aspose.Cells FOSS for .NET is published under the MIT license. The package is distributed via NuGet as Aspose.Cells_FOSS. MIT licensing permits use in both open-source and commercial projects with no royalties or restrictions on redistribution.

Getting Started