10 .NET Developer Insights from May 2026 You Can't Afford to Miss

Welcome to this fresh take on the latest .NET community buzz! We've sifted through the May 2026 dotInsights newsletter to bring you ten standout insights that every .NET developer should know. From performance tricks and AI-assisted coding debates to cutting-edge frameworks and security warnings, this listicle distills the month's most valuable content into digestible takeaways. Whether you're a seasoned architect or just starting out, these items will sharpen your skills and keep you ahead of the curve. Let's dive in.

1. C# Ref Returns and Ref Locals: Work with Variables, Not Copies

C# has a hidden gem: ref returns and ref locals. Instead of returning a copy of a value from a method, you can return a reference to the original variable. This means you can directly modify that variable without extra allocations or copying. For example, you can create an array-like structure where ref return allows you to get a reference to an element and then manipulate it inline. The result? Performance gains in hot paths and reduced memory pressure. It's especially powerful when working with large structs or tight loops. If you haven't explored this feature yet, check out the original dotInsights entry for deeper examples.

2. Stop Writing Specs – Let AI Interrogate You Instead

In a thought-provoking video, Gui Ferreira challenges the traditional approach of writing detailed specifications. Instead, he proposes using AI to interview you about requirements. By answering a series of smart questions, the AI generates a precise spec – saving hours of manual documentation. This method reduces ambiguity and ensures you cover edge cases. Ferreira argues that the human-AI collaboration leads to clearer, more testable outcomes. It's a paradigm shift that could redefine how teams gather and document requirements. Watch the full talk to see it in action.

3. Speed Up Your AI Development Workflow by 2x

Nick Chapsas shares hands-on tips to turbocharge AI integration in .NET projects. From leveraging IChatClient to optimizing prompt pipelines, his session shows concrete ways to cut development time in half. One key takeaway: use structured output formats (like JSON schemas) to get reliable responses from LLMs. Another is to batch similar requests to reduce overhead. If you're building AI-powered features in your C# apps, this video is a goldmine of actionable techniques.

4. Testable Code Doesn't Mean 'Interfaces Everywhere'

Derek Comartin (CodeOpinion) debunks the myth that testability requires a proliferation of interfaces. He demonstrates how to write clean, testable code using concrete classes, dependency injection, and functional patterns. The key is to design for seams – places where you can inject test doubles – without forcing every class to implement an interface. This pragmatic approach reduces ceremony while keeping your tests fast and maintainable. It's a must-watch for anyone tired of interface-heavy architectures.

5. Removing byte[] Allocations in .NET Framework Using ReadOnlySpan<T>

Andrew Lock dives into practical memory optimization by replacing byte[] allocations with ReadOnlySpan<T> in .NET Framework projects. Even though Span wasn't originally available in older frameworks, Lock shows how to backport it using the System.Memory NuGet package. The result: zero allocations in many parsing and processing scenarios, leading to faster code and less GC pressure. This technique is especially valuable for high-throughput services still running on .NET Framework.

6. The Cookie Apocalypse Already Happened – What That Means for Developers

Khalid Abuhakmeh explains that the much-feared 'cookiepocalypse' (browsers phasing out third-party cookies) is already here, and many sites are still unprepared. He outlines practical steps for .NET developers: adopt server-side tracking, leverage first-party data, and use privacy-preserving APIs like CHIPS and Federated Credential Management. The article also covers how to update your ASP.NET Core apps to work without third-party cookies. Ignoring this shift could break analytics and ad-revenue dependencies. Read the full piece to future-proof your web applications.

7. Does Code Quality Still Matter in the Age of AI-Assisted Coding?

Mark Heath tackles a burning question: as AI tools generate more code, do human code quality standards become obsolete? His answer: absolutely not. He argues that AI-generated code often lacks context, introduces subtle bugs, and creates comprehension debt (a term popularized by Addy Osmani). Heath urges developers to review AI output rigorously, enforce coding standards via analyzers, and continue investing in clean architecture. The article includes practical tips for integrating AI while maintaining high-quality codebases.

8. EF Core: Delete and Update Millions of Rows Without Loading Entities

Chris Woodruff reveals a devastating performance trick for Entity Framework Core: directly executing bulk operations using ExecuteUpdate and ExecuteDelete. Instead of loading millions of rows into memory, you can issue a single SQL statement that updates or deletes based on a condition. This approach slashes memory usage and execution time. Woodruff also discusses pitfalls like transaction scope and change tracking. If you manage large datasets with EF Core, this is an essential read.

9. URL Pattern Matching in .NET – A New Power for Routing

Gérald Barré introduces a new API for URL pattern matching in .NET, enabling more flexible routing rules. You can now match complex URL patterns, extract parameters, and even validate against custom patterns without relying on regex. This feature integrates seamlessly with ASP.NET Core and is useful for middleware, reverse proxy handling, and custom endpoint selection. Barré provides code examples showing how to harness UrlPattern for both simple and advanced scenarios.

10. The Toolkit Pattern – Reusable, Composable Code for .NET

Andrew Stellman presents the Toolkit Pattern: a way to build reusable, composable libraries that follow consistent conventions. Instead of monolithic frameworks, create small, focused toolkits that can be mixed and matched. Each toolkit solves a specific problem (logging, validation, telemetry) and exposes a fluent API. Stellman shows how to design them using dependency inversion, null-object patterns, and extension methods. The result is a maintainable, testable set of building blocks that evolve independently.

Conclusion

From advanced C# features to AI workflow hacks and security insights, the May 2026 dotInsights newsletter packed a punch. We've covered ten topics that represent the pulse of .NET development right now. Whether you're optimizing memory with spans, rethinking specs with AI, or tackling the cookie apocalypse, these insights will keep your skills sharp and your applications modern. Don't forget to explore the linked talks and articles for deeper dives. Happy coding!