More examples

IUtf8SpanFormattable support (.net8+)

Effective way to write standard and custom types to cell without string allocation.

//write any IUtf8SpanFormattable value as string cell or numeric cell
//format, format provider and styles are optional

writer.AddCellString(Guid.NewGuid(), ['N']);  

float value = 0.3f;
writer.AddCellNumber(value);

Interpolated strings (.net8+)

Writing interpolated strings to cells without allocations (benchmark).

writer.AddCell($"{person.FirstName} {person.LastName}, age {person.Age}");
writer.AddCell($"Now is {DateTime.Now}");  

Write Excel file to Http response

The data isn't accumulated in memory. It is flushed to Http response streamingly.

Response.ContentType = "application/vnd.openxmlformats-officedocument.spreadsheetml.sheet";
Response.Headers.Add("Content-Disposition", $"attachment; filename=fileName.xlsx");

await Response.StartAsync();

await using var writer = new ExcelWriter(Response.BodyWriter.AsStream(), token: cancellationToken);

await writer.StartSheet("Sheet name");
await writer.StartRow();
writer.AddCell(123);

await writer.Complete();

Row Attributes

//add row with specified height
await writer.StartRow(height: 15);

//or specify optional row attributes
await writer.StartRow(new RowAttributes(
    Height: 25, 
    OutlineLevel: 1,
    IsCollapsed: true,
    IsHidden: true)); 

Using styles

// 1. Define styles

var styleBuilder = new StylesSheetBuilder();

staticSomeStyle = styleBuilder.GetOrAdd(
    new Style(
        Format: "0.00%", // or StandardFormat.PercentPrecision2
        Font: new Font(Size: 24, Color: Color.DodgerBlue),
        Fill: new Fill(Color: Color.Crimson, FillPattern.Gray125),
        Borders: new Borders(
            Left: new Border(BorderStyle.Thick, Color.BlueViolet),
            Right: new Border(BorderStyle.MediumDashed, Color.Coral)),
        Alignment: new Alignment(HorizontalAlignment.Center, VerticalAlignment.Center, false)));

// 2. Build styles. We can reuse single style sheet many times to increase performance. 
//    Style sheet is immutable and thread safe.

staticStyleSheet = styleBuilder.Build();

// 3. Using styles

await using var writer = new ExcelWriter(file, staticStyleSheet);

await writer.StartSheet("First sheet");
await writer.StartRow(15); //optional row height specified

writer.AddCell(123, staticSomeStyle);  // all cells support style reference

await writer.Complete();

Format property can be string, int (any valid numFmtId) or StandardFormat enum value

Shared strings

Shared strings decrease the size of the resulting file when it contains repeated strings. It's implemented as unique list of strings, and cell contains only reference to the list index.

// 1. We can use global shared strings table

var tableBuilder = new SharedStringTableBuilder();

staticSharedStringRef1 = tableBuilder.GetOrAdd("String");
staticSharedStringRef2 = tableBuilder.GetOrAdd("Another String");

// 2. Build table

staticSharedStringTable = sharedStringTableBuilder.Build();

// 3. Using shared strings

await using var writer = new ExcelWriter(stream, sharedStringTable: staticSharedStringTable);

await writer.StartSheet("First sheet");
await writer.StartRow();

// using refernce from global table
writer.AddCell(staticSharedStringRef1);  
writer.AddCell(staticSharedStringRef2);  

// using local dictionary automatically maintained in the ExcelWriter instance
writer.AddCellSharedString("Some string from exteranal store");
writer.AddCellSharedString("Some string from exteranal store");

await writer.Complete();

Benchmarks & performance

Benchmarks results and source code.

Please note .net 9 can be 2x faster than .net 8 for some cases.
Benchmarks below use .net 9.0 runtime.

Real world report

100 columns: numbers, dates, strings

OpenXML and SpreadCheetah comparison

Full results and benchmark code.