ExcelLite 0.5.0

📦 ExcelLite – Lightweight Open Source Excel Generator for .NET

ExcelLite is an open-source C# library designed for fast and memory-efficient generation of Excel (Open XML) files. It focuses on simplicity and performance, making it ideal for scenarios where massive Excel files need to be created with minimal memory overhead.

🚀 Key Features

• ✅ Minimalistic API – Simple and intuitive interface for quick integration and easy use.
• 🧠 Low RAM usage – Designed to avoid keeping the entire document in memory.
• ⚡ High performance – Easily generates large-scale Excel files.
• 🔁 Async streaming support — fully supports IAsyncEnumerable<T> for generating spreadsheets from asynchronous data sources.
• 🧩 Nested class support — easily export complex hierarchical objects into structured Excel sheets.
• 📄 Open XML compliant – Outputs standard .xlsx files.
• 📦 No external dependencies – Lightweight and dependency-free by default.
• 🌍 Developed 100% in Europe – Ensures full compliance with regional legal, security, and privacy requirements (e.g. GDPR).

💡 Why Use ExcelLite?

Most existing Excel libraries load the entire workbook into memory, which can be problematic when exporting large datasets. ExcelLite takes a streaming approach, writing XML directly to the output stream, allowing you to generate Excel files with millions of rows without overwhelming system resources.

This makes it perfect for:

• Generating large reports
• Web APIs
• Background jobs
• Cloud or serverless environments with limited RAM
• Exporting massive datasets from databases or logs
• Background/batch processing where performance and memory usage matter
• Compliance-conscious environments where software origin matters

📊 Performance Comparison with Other Libraries

Test - 12 columns and 1000000 rows | Method | Mean | Error | StdDev | Gen0 | Gen1 | Gen2 | Allocated | |------------------- |--------:|--------:|--------:|-------------:|----------:|----------:|----------:| | ExcelLiteBenchmark | 15.42 s | 0.209 s | 0.196 s | 855000.0000 | 1000.0000 | - | 1.25 GB | | MiniExcelBenchmark | 18.59 s | 0.183 s | 0.162 s | 4592000.0000 | 3000.0000 | 2000.0000 | 6.72 GB |

Test - 12 columns and 1000 rows | Method | Mean | Error | StdDev | Gen0 | Gen1 | Gen2 | Allocated | |------------------- |----------:|----------:|----------:|-----------:|-----------:|----------:|----------:| | ExcelLiteBenchmark | 14.81 ms | 0.295 ms | 0.532 ms | 843.7500 | - | - | 1.27 MB | | MiniExcelBenchmark | 26.43 ms | 0.525 ms | 0.625 ms | 5656.2500 | 1343.7500 | 1093.7500 | 21.97 MB | | ClosedXMLBenchmark | 821.38 ms | 16.190 ms | 35.537 ms | 66000.0000 | 17000.0000 | 3000.0000 | 186.17 MB |

🛠 Example Use Case

Generate simple file

          var data = new List<TestClass>()
            {
                new TestClass
                {
                    FirstName = "Jan",
                    LastName = "Nowak",
                    Income = 6000,
                    Float = 34.232f,
                    Street="asdasdasdasdasdas"
                },
                new TestClass
                {
                    FirstName = "Jan",
                    LastName = "Kowalski",
                    Income = 7000,
                    Float = 34.232f,
                    OtherBoolean = true,
                    DateTime= DateTime.Now,
                    TimeOnly = new TimeOnly(21,37,00),
                    DateOnly = new DateOnly(2025,07,01)
                },
            };

            await ExcelLite.Export("test.xlsx", data);

Generate 2 sheets in one file with freeze panes

        var data = new List<TestClass>()
            {
                new TestClass
                {
                    FirstName = "Jan",
                    LastName = "Nowak",
                    Income = 6000,
                    Float = 34.232f,
                    Street="asdasdasdasdasdas"
                },
                new TestClass
                {
                    FirstName = "Jan",
                    LastName = "Kowalski",
                    Income = 7000,
                    Float = 34.232f,
                    OtherBoolean = true,
                    DateTime= DateTime.Now,
                    TimeOnly = new TimeOnly(21,37,00),
                    DateOnly = new DateOnly(2025,07,01)
                },
            };

            var data2 = new List<SalaryTestClass>()
            {
                new SalaryTestClass
                {
                    FirstName = "Jan",
                    LastName = "Nowak",
                    Income = 6000
                },
                new SalaryTestClass
                {
                    FirstName = "Jan",
                    LastName = "Kowalski",
                    Income = 6100
                },
                new SalaryTestClass
                {
                    FirstName = "Jan",
                    LastName = "Adamczewski",
                    Income = 6200
                }
            };

            var sheet1 = new Sheet("Arkusz1", data);
            sheet1.View.FreezePanes.YSplit = 3;

            await ExcelLite.Export("test.xlsx", new Workbook(new Sheet[] { new Sheet("Salary", data2), sheet1  }));

Example attributes

    public class TestClass
    {
        [GroupColumnName("Personal data", 0)]
        [GroupColumnName("First and Last Name", 1)]
        public string FirstName { get; set; }

        [GroupColumnName("Personal data", 0)]
        [GroupColumnName("First and Last Name", 1)]
        public string LastName { get; set; }

        [GroupColumnName("Personal data", 0)]
        public int Income { get; set; }


        [ColumnName("CustomName")]
        [ColumnFormat("00.00")]
        public float Float { get; set; }

        //[ColumnPosition(2)]
        public bool OtherBoolean { get; set; }

        [GroupColumnName("Address", 1)]
        public string Street { get; set; }

        [GroupColumnName("Address", 1)]
        public string City { get; set; }

        [GroupColumnName("Address", 1)]
        public string PostalCode { get; set; }

        [GroupColumnName("Address", 1)]
        public string BuildingNumber { get; set; }

        public DateTime DateTime { get; set; }

        public DateOnly DateOnly { get; set; }

        public TimeOnly TimeOnly { get; set; }
    }

Record usage

   var data = Enumerable.Range(0, 100).Select(x => new RecordT("abc", "def", x));
   await ExcelLite.Export("test.xlsx", data);

IAsyncEnumerable usage

        public static async Task AsyncEnumerableTest()
        {
            await ExcelLite.Export("test.xlsx", TestAsyncEnumerable());
        }

        private static async IAsyncEnumerable<RecordT> TestAsyncEnumerable()
        {
            for (int i = 1; i <= 60; i++)
            {
                await Task.Delay(10);
                yield return new RecordT("abc", "def", i); 
            }
        }

📄 License

MIT License © 2025 Krzysztof Kończak