Writing High-Performance Code in .NET: Best Practices for Developers

Writing clean and functional code is important—but writing high-performance code is what truly sets great developers apart. Whether you’re building APIs, desktop apps, or background services in .NET, performance matters. It affects user experience, scalability, and infrastructure cost.

In this article, we’ll explore practical tips and best practices for writing efficient and performant .NET code.

1. Use Asynchronous Programming

Blocking threads can significantly hurt scalability, especially in web applications. Instead of synchronous methods, prefer async/await.


// Bad
var result = httpClient.GetStringAsync(url).Result;

// Good
var result = await httpClient.GetStringAsync(url);

Use ConfigureAwait(false) where you don’t need context switching (e.g., in libraries).

2. Avoid Unnecessary Allocations

Frequent allocations trigger the garbage collector (GC), which can cause performance hiccups. Avoid:

• Using new inside tight loops

• Creating temporary lists or arrays unnecessarily

• Boxing value types (e.g., using object instead of int)

• Using LINQ where performance is critical

Example:

// Expensive in large loops
var filtered = list.Where(x => x.IsActive).ToList();

// Prefer a manual loop for critical paths
var filtered = new List();
foreach (var item in list)
{
if (item.IsActive) filtered.Add(item);
}

3. Use Span<T> and Memory<T> for Low-Level Operations

For processing large arrays, strings, or byte buffers, use Span<T> or Memory<T> to avoid unnecessary allocations and copies.

ReadOnlySpan dataSpan = new ReadOnlySpan(buffer);

These types are stack-allocated, super fast, and ideal for performance-critical code.

4. Cache Repeated Expensive Operations

Avoid repeating costly operations like regex parsing, reflection, or database lookups. Use caching patterns like:

• MemoryCache or IMemoryCache for in-memory caching

• ConcurrentDictionary for thread-safe lookups

• Lazy initialization for expensive objects

5. Profile, Measure, and Benchmark

Use profiling tools to find real bottlenecks:

• BenchmarkDotNet for micro-benchmarking

• dotTrace, PerfView, or Visual Studio Profiler

• MiniProfiler for web request performance

Avoid optimizing prematurely—measure first, optimize second.

Final Thoughts

Performance tuning in .NET isn’t about writing “clever” code—it’s about understanding the runtime, memory usage, and execution patterns.

By applying async patterns, reducing allocations, caching smartly, and profiling your code regularly, you can deliver faster and more efficient applications that scale better and cost less to run.

Performance is a feature—design for it from day one.