SpreadSheetTasks

The .NET library for fast reading and writing Excel files (.xlsx, .xlsb).

Installation

dotnet add package SpreadSheetTasks

<PackageReference Include="SpreadSheetTasks" Version="1.0.0" />

Quick Start

Write to Excel

using SpreadSheetTasks;
using System.Data;

var dt = new DataTable();
dt.Columns.Add("Name", typeof(string));
dt.Columns.Add("Age", typeof(int));
dt.Rows.Add("Alice", 30);
dt.Rows.Add("Bob", 25);

using (var writer = new XlsxWriter("output.xlsx")) // or XlsbWriter
{
    writer.AddSheet("People");
    writer.WriteSheet(dt.CreateDataReader());
}

Read from Excel

using SpreadSheetTasks;

using (var reader = new XlsxOrXlsbReadOrEdit())
{
    reader.Open("output.xlsx");
    reader.ActualSheetName = "People";

    object[]? row = null;
    while (reader.Read())
    {
        row ??= new object[reader.FieldCount];
        reader.GetValues(row);
    }
}

Documentation

Full usage guide with detailed examples:

• docs/index.md

Write from object[][] (typed headers)

using SpreadSheetTasks;

using (var writer = new XlsxWriter("products.xlsx"))
{
    writer.AddSheet("Products");
    writer.WriteSheet(
        rows: new object[][]
        {
            new object[] { "Apple", 1.99, 100 },
            new object[] { "Banana", 0.99, 250 },
        },
        headers: new[] { "Product", "Price", "Quantity" },
        headers_row: true,
        doAutofilter: true
    );
}

Write with per-cell formatting (FormattedCell[][])

using SpreadSheetTasks;

using (var writer = new XlsxWriter("formatted.xlsx"))
{
    writer.AddSheet("Sheet1");
    writer.WriteSheet(
        rows: new object[][]
        {
            new object[] { 1234567, 1234.56 },
            new object[] { 0.25, 12345.67 },
        },
        headers: new[] { "Thousands", "Scientific" },
        formats: new FormattedCell[][]
        {
            new FormattedCell[] { new(1234567, F.THOUSANDS_SEP), new(1234.56, F.CURRENCY_PLN) },
            new FormattedCell[] { new(0.25, F.PERCENTAGE), new(12345.67, F.SCIENTIFIC) },
        }
    );
}

GetExcelDataType / GetNativeValue

using SpreadSheetTasks;

using (var reader = new XlsxOrXlsbReadOrEdit())
{
    reader.Open("data.xlsx");
    reader.ActualSheetName = "Sheet1";

    while (reader.Read())
    {
        // Use typed getters for general use
        string name = reader.GetString(0);
        long value = reader.GetInt64(1);

        // Use GetExcelDataType to inspect cell type
        ExcelDataType type = reader.GetExcelDataType(2);

        // High-performance escape hatch (check type first!)
        if (type == ExcelDataType.Double)
        {
            double raw = reader.GetNativeValue(2).doubleValue;
        }
    }
}

Update existing XLSX (ReplaceSheetData + ReplacePivotTableDim)

using SpreadSheetTasks;
using System.Data;

using (var reader = new XlsxOrXlsbReadOrEdit())
{
    reader.Open("existing.xlsx", updateMode: true);

    var newData = new DataTable();
    newData.Columns.Add("Product", typeof(string));
    newData.Columns.Add("Revenue", typeof(decimal));
    newData.Rows.Add("Widget", 50000m);

    // Replace data in a sheet
    string range = reader.ReplaceSheetData("Sheet1", newData.CreateDataReader());

    // Update pivot table data source reference
    reader.ReplacePivotTableDim("PivotTable1", range);
}

Write to existing Stream (XlsxWriter.WriteToExisting)

using SpreadSheetTasks;
using System.Data;
using System.IO;
using System.IO.Compression;

// Open an existing xlsx as a ZipArchive and write into a sheet stream
using (var archive = ZipFile.Open("existing.xlsx", ZipArchiveMode.Update))
{
    var entry = archive.GetEntry("xl/worksheets/sheet1.xml");
    using var writer = new StreamWriter(entry.Open());

    var dt = new DataTable();
    dt.Columns.Add("Name", typeof(string));
    dt.Rows.Add("Alice");

    int rowsWritten = XlsxWriter.WriteToExisting(writer, dt.CreateDataReader());
}

Stream writer with custom buffer size

using SpreadSheetTasks;
using System.Data;

// Larger buffer for better write throughput on large files
using (var writer = new XlsxWriter("large.xlsx", bufferSize: 65536))
{
    writer.AddSheet("Data");
    var dt = new DataTable();
    dt.Columns.Add("Col", typeof(string));
    for (int i = 0; i < 100_000; i++) dt.Rows.Add($"Row{i}");
    writer.WriteSheet(dt.CreateDataReader());
}

Breaking Changes in v1.0.0

Old (v0.6.1)	New (v1.0.0)
GetScheetNames() (typo)	GetSheetNames()
DocPopertyProgramName (typo)	DocPropertyProgramName
SuppressSomeDate	SuppressYear1000Dates
overLimit parameter	maxRows parameter
RowCount returns 123123123 for unknown	RowCount returns -1 for unknown
FormattingStreamWriter (public)	FormattingStreamWriter (internal)
UseMemoryStreamInXlsb (field)	UseMemoryStreamInXlsb (property)
Duplicate F.SHORT_DATE etc. constants	Marked [Obsolete]

Old names still compile with [Obsolete] warnings.

Benchmarks

Windows 11 (25H2), AMD Ryzen 7 7840HS, .NET 10.0.8, BenchmarkDotNet 0.15.8

XLSB Read (65k rows)

Method	Mean	Error	StdDev	Gen0	Gen1	Gen2	Allocated
'SpreadSheetTasks - XLSB Read - v1' (quick)	52.56 ms	3.121 ms	0.17 ms	2400.0000	800.0000	700.0000	28.93 MB
'SpreadSheetTasks - XLSB Read - v2' (quick)	60.61 ms	67.866 ms	3.72 ms	1666.6667	-	-	13.76 MB

XLSX Read (65k rows, typed getters)

Method	Mean	Error	StdDev	Allocated
SpreadSheetTasks65k	178.2 ms	124.7 ms	6.83 ms	593.92 KB

XLSB Write (50k rows, mixed types)

Method	ReaderType	Mean	Error	StdDev	Gen0	Gen1	Gen2	Allocated
'SpreadSheetTasks - XLSB Write'	GENERAL	40.40 ms	13.952 ms	0.77 ms	916.6667	166.6667	83.3333	10.86 MB
XlsbSylvanWrite	GENERAL	51.34 ms	12.901 ms	0.71 ms	545.4545	181.8182	90.9091	8.98 MB

XLSX Write (50k rows, mixed types)

Method	ReaderType	Mean	Error	StdDev	Gen0	Gen1	Gen2	Allocated
'SpreadSheetTasks - XLSX Write'	GENERAL	58.08 ms	8.808 ms	0.48 ms	1111.1111	111.1111	-	13.31 MB
XlsxSylvanWrite	GENERAL	73.63 ms	73.330 ms	4.02 ms	571.4286	142.8571	-	10.51 MB

macOS Tahoe 26.5.1 (Apple M4), .NET 10.0.8, BenchmarkDotNet 0.15.8

XLSB Read (65k rows)

Method	Mean	Error	StdDev	Gen0	Gen1	Gen2	Allocated
'SpreadSheetTasks - XLSB Read - v1' (quick)	40.56 ms	2.895 ms	1.59 ms	2461.5385	846.1538	769.2308	28.93 MB
'SpreadSheetTasks - XLSB Read - v2' (quick)	47.62 ms	3.617 ms	1.98 ms	1666.6667	-	-	13.76 MB

XLSX Read (65k rows, typed getters)

Method	Mean	Error	StdDev	Allocated
SpreadSheetTasks65k	152.3 ms	1.29 ms	1.01 ms	593.88 KB

XLSB Write (50k rows, mixed types)

Method	ReaderType	Mean	Error	StdDev	Gen0	Gen1	Gen2	Allocated
'SpreadSheetTasks - XLSB Write'	GENERAL	23.97 ms	0.178 ms	0.166 ms	968.7500	187.5000	93.7500	10.86 MB
XlsbSylvanWrite	GENERAL	32.48 ms	0.509 ms	0.425 ms	562.5000	187.5000	125.0000	8.98 MB

XLSX Write (50k rows, mixed types)

Method	ReaderType	Mean	Error	StdDev	Gen0	Gen1	Gen2	Allocated
'SpreadSheetTasks - XLSX Write'	GENERAL	41.43 ms	0.781 ms	0.731 ms	1230.7692	230.7692	-	13.31 MB
XlsxSylvanWrite	GENERAL	41.18 ms	0.495 ms	0.386 ms	750.0000	250.0000	83.3333	10.51 MB

Links

• NuGet: https://www.nuget.org/packages/SpreadSheetTasks/
• GitHub: https://github.com/KrzysztofDusko/SpreadSheetTasks
• License: MIT