Training course · OpenAI Codex · C# & .NET

OpenAI Codex for C# and .NET Developers

Delegate development work with OpenAI Codex: CLI and cloud agent, AGENTS.md, sandboxing, approvals and team PR workflows.

Duration
2 days (14 hrs)
Format
Online or on-site
Language
German or English
Participants
open dates or exclusive for your team
Certificate
Certificate of attendance

Overview

“OpenAI Codex for C# and .NET Developers” is a hands-on course for roles such as C# developers working with ASP.NET Core, Blazor or WPF, Teams migrating applications from .NET Framework to modern .NET and Software architects for .NET and Azure solutions. Rather than learning OpenAI Codex in the abstract, you work on tasks from your daily routine – with examples, exercises and templates from C# & .NET.

OpenAI Codex is a coding agent that runs both locally, as a command-line tool and IDE extension, and as a cloud agent. Locally, Codex reads your repository, proposes changes and runs commands inside a sandboxed environment. In the cloud, it works on delegated tasks in parallel inside isolated containers and returns results as traceable diffs or pull requests. Over two days you will learn how to combine both modes effectively and how to scope tasks so that the agent can complete them reliably and with minimal back-and-forth.

Control and security sit at the heart of the course. With AGENTS.md you hand Codex project knowledge, build and test commands, and conventions. You configure approval modes and sandboxing so that the agent only does what you permit, and you set up cloud environments with suitable setup scripts. You will also integrate Codex into your pull request workflows, use automated code review, and define team rules on which tasks are delegated and how results are checked before they are merged into the main branch.

C# and .NET are firmly established in many organisations: ASP.NET Core APIs, Blazor and WPF front ends, Azure services and line-of-business applications dating back to the .NET Framework era. Migrating from the classic .NET Framework to modern cross-platform .NET in particular ties up significant capacity. AI coding assistants and agents take over much of the mechanical work here: converting project files to SDK style, identifying WCF or Web Forms dependencies, writing xUnit or NUnit tests, optimising Entity Framework Core queries and introducing nullable reference types. To do this well, they need context on solution structure, analyser rules and architectural guidelines. This course shows you how to use agents in Visual Studio, VS Code or Rider and on the command line.

The course is delivered live – either online in a virtual classroom or on-site in our training rooms in Munich, Salzburg, Berlin, Augsburg, Hanover, Bremen, Stuttgart and Kaiserslautern. We can also run it exclusively for your team.

Who is this course for?

  • C# developers working with ASP.NET Core, Blazor or WPF
  • Teams migrating applications from .NET Framework to modern .NET
  • Software architects for .NET and Azure solutions
  • Developers of line-of-business applications in industry and SMEs

Typical challenges we address

  • Costly migration of .NET Framework applications built on WCF, Web Forms or ageing NuGet packages
  • Large solutions with many projects, circular dependencies and little test coverage
  • Performance issues caused by inefficient Entity Framework queries
  • Inconsistent handling of nullability, async/await and dependency injection

What you will be able to do

  • You use Codex locally and in the cloud for the development tasks each mode suits best.
  • You write an AGENTS.md that guides the agent reliably through your project.
  • You configure approval modes and sandboxing to match your security requirements.
  • You delegate tasks to the cloud agent and review the results systematically.
  • Use AI agents for .NET migrations, refactorings and test generation across large solutions.
  • Optimise Entity Framework Core data access and ASP.NET Core APIs with AI support.
  • Define analyser rules, conventions and review criteria that generated C# code meets reliably.

Course outline

Day 1

Module 1 Codex at a glance: CLI, IDE and cloud
  • Comparing how Codex works locally and in the cloud
  • Installing the Codex CLI, signing in and starting it in a repository
  • Interactive sessions, non-interactive execution and model choice
  • Distinguishing tasks that suit a coding agent from those that do not
Module 2 Project knowledge with AGENTS.md
  • Building an AGENTS.md with build, test and lint commands
  • Stating conventions, architectural notes and prohibitions precisely
  • Using nested AGENTS.md files for monorepos and sub-projects
  • Checking effectiveness and refining instructions iteratively
Module 3 Sandboxing, approvals and security
  • Choosing approval modes deliberately, from read-only to largely autonomous
  • Understanding sandbox boundaries for file system and network access
  • Handling secrets, dependencies from the internet and prompt injection
  • Configuration files for team standards and safe defaults
Module 4 Delegating tasks to the cloud agent
  • Configuring cloud environments with setup scripts and dependencies
  • Writing tasks with a clear goal, context and acceptance criteria
  • Launching several tasks in parallel and comparing the results
  • Using logs and test output to understand the proposed solutions

Day 2

Module 5 PR workflows and code review in the team
  • Turning results into pull requests and requesting follow-up changes
  • Using automated Codex code review on GitHub
  • Embedding Codex in scripts and CI pipelines
  • Setting team rules for delegation, review duties and accountability
Module 6 Practice lab: C# & .NET
  • Migrating to modern .NET
  • Writing xUnit and NUnit tests
  • Optimising Entity Framework Core
  • Introducing nullable reference types
  • Building ASP.NET Core APIs
  • Code analysis and refactoring
Module 7 Data protection, quality & transfer to daily work
  • Clarify whether source code may be sent to cloud models and which tenant or region settings apply, and keep connection strings and secrets from User Secrets or Key Vault out of prompts. New NuGet packages should be checked for licence, provenance and vulnerabilities – not least in view of the obligations under the Cyber Resilience Act.
  • Ground rules for safe AI use in your team
  • Checking results: facts, sources, tests and the four-eyes principle
  • Personal action plan for the next 30 days
  • Open questions, outlook and resources for further learning

Practical scenarios from your field

Migrating to modern .NET

The agent analyses projects using the upgrade tooling and compiler output, converts csproj files to SDK style, replaces incompatible APIs and proposes alternatives to WCF or System.Web until the solution builds and tests pass.

Writing xUnit and NUnit tests

Services, controllers and domain logic get unit tests with Moq or NSubstitute plus integration tests using WebApplicationFactory. The AI covers edge cases and sticks to your existing test conventions.

Optimising Entity Framework Core

The AI analyses generated SQL, spots N+1 problems, missing AsNoTracking calls or awkward Includes, and creates migrations and projections for faster queries. Every change is backed by the resulting SQL.

Introducing nullable reference types

Nullable is enabled project by project while the AI works through compiler warnings, adds guard clauses and annotations and makes implicit assumptions in the code explicit.

Building ASP.NET Core APIs

Specifications become minimal APIs or controllers with validation, ProblemDetails error handling, authentication and OpenAPI documentation, consistent with your existing layered architecture. Integration tests safeguard each new endpoint.

Code analysis and refactoring

Roslyn analyser findings are fixed systematically, oversized classes split, async anti-patterns such as .Result removed and dependency injection registrations made consistent. Build, analysers and existing tests confirm that behaviour is unchanged.

Possible hands-on projects

Minimal API service

An ASP.NET Core service using minimal APIs, EF Core, health checks, structured logging and integration tests, built end to end by an AI agent from a specification.

Migration inventory

A console tool that scans a solution, lists target frameworks, NuGet packages and incompatible APIs, and produces a prioritised migration plan.

Blazor admin UI

A small Blazor application for managing master data, with form validation, filterable tables and integration with an existing REST API.

Prerequisites

You have hands-on programming experience, are comfortable with Git and the command line, and know pull-request-based workflows. Good C# skills, experience with ASP.NET Core or .NET desktop development, and familiarity with Visual Studio, Rider or VS Code and Git.

Technical requirements

Your own laptop with a terminal, Git and a Node.js runtime; a ChatGPT plan with Codex access or an OpenAI API key, plus a GitHub account for the cloud exercises.

Data protection & compliance

Clarify whether source code may be sent to cloud models and which tenant or region settings apply, and keep connection strings and secrets from User Secrets or Key Vault out of prompts. New NuGet packages should be checked for licence, provenance and vulnerabilities – not least in view of the obligations under the Cyber Resilience Act.

Suggested dates

All dates are suggestions – your preferred date is always possible.

  • Tue, 24 November 2026 – Wed, 25 November 2026 Online Request
  • Wed, 2 December 2026 – Thu, 3 December 2026 Munich Request
  • Thu, 10 December 2026 – Fri, 11 December 2026 Online Request
  • Mon, 18 January 2027 – Tue, 19 January 2027 Online Request
  • Wed, 27 January 2027 – Thu, 28 January 2027 Berlin Request
  • Tue, 2 February 2027 – Wed, 3 February 2027 Online Request

Frequently asked questions

When should I use Codex locally and when in the cloud?

Locally you work interactively and close to the code, for example when debugging or making exploratory changes where you want to follow every step. The cloud agent suits well-defined tasks that can run independently, such as adding tests or fixing smaller bugs. You can start several of these in parallel and review each one as a pull request.

What belongs in a good AGENTS.md?

A good AGENTS.md explains how the project is built, tested and checked, which conventions apply and which areas must not be touched. It is concise, concrete and kept up to date. Notes on architecture and common pitfalls also help. During the course you write an AGENTS.md for a project of your own and test how it changes the agent’s behaviour.

How safe is it to let Codex run commands?

By default Codex works inside a sandbox with restricted file and network access and asks for approval before risky steps. You decide how much autonomy to grant through approval modes and configuration. In the course you learn to choose these settings deliberately and to limit risks such as prompt injection or running unfamiliar dependencies.

Does AI really help with migrating from .NET Framework?

Yes, especially with the mechanical work: converting project files, finding incompatible APIs, suggesting replacement libraries and fixing build errors iteratively. Fundamental architecture decisions, such as replacing WCF with gRPC or REST, remain with the team. On the course you practise breaking such migrations into small, verifiable steps.

Do AI agents work with Visual Studio?

Many AI assistants integrate directly with Visual Studio, VS Code or Rider, while others run in the terminal alongside the dotnet CLI. The methods taught are tool-neutral: you learn to provide context, scope tasks and safeguard results through builds, analysers and tests, regardless of your IDE.

How much does “OpenAI Codex for C# and .NET Developers” cost?

The course costs a flat €949 plus VAT per participant – whether online or on-site. This includes 2 training day(s) with a live trainer, course materials, a lab environment and a certificate of attendance.

Can I suggest my own date?

Yes. Our suggested dates are just a guide. In the request form you can always describe your preferred date or period in free text – we check availability and confirm within one working day.

Is the course online or on-site?

Both are possible: live online in a virtual classroom or on-site in Munich, Salzburg, Berlin, Augsburg, Hanover, Bremen, Stuttgart or Kaiserslautern. We can also run the course exclusively for your team.

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