LegacyDotnetAgentKit

LegacyDotnetAgentKit is a practical starter kit for agent-assisted legacy .NET modernization.

It helps teams use coding agents to modernize WPF, WinForms, ASP.NET, custom server-call, and older .NET systems without losing hidden business rules, security behavior, or user workflows.

The first release is intentionally not a runtime NuGet package. Most legacy migration failures come from missed system contracts rather than missing helper methods. This kit starts with the repeatable workflow: inspect the source, map current behavior, identify risky boundaries, split changes into reviewable slices, and state verification limits clearly.

What is included

• A Codex-compatible skill in skills/legacy-dotnet-agent-kit/
• Reference guides for intake, risk patterns, migration slicing, verification, and agent handoff
• Templates for architecture maps, behavior maps, risk registers, slice plans, test matrices, feedback logs, and rewrite boundary assessments
• Generic examples for common legacy .NET modernization scenarios

Who this is for

This kit is for engineering teams that already have a legacy .NET system and want a coding agent to help with modernization safely. It is especially useful when the codebase has:

• UI code mixed with persistence, server calls, or workflow logic
• custom security or data-scope rules
• cache and async behavior that changed over time
• old reporting stacks such as RDLC or WinForms-hosted report viewers
• incomplete local build or test environments
• knowledge spread across code, docs, tickets, and developer memory

Core workflow

1. Read repo-local instructions and collaboration notes.
2. Map the current behavior from source before proposing changes.
3. Identify security, workflow, persistence, cache, and UI ownership boundaries.
4. Build a migration risk register.
5. Choose one small, behavior-preserving modernization slice.
6. Implement only after the slice has clear acceptance criteria.
7. Verify what can be verified, and name what remains unverified.
8. Leave durable notes for the next developer or agent.

Install The Skill

The GitHub repository is:

https://github.com/Mohrimn/legacy-dotnet-agent-kit.git

The install commands below will work after the repository contents have been pushed.

Recommended: ask Codex to install it

In Codex, ask:

Install the skill from https://github.com/Mohrimn/legacy-dotnet-agent-kit/tree/main/skills/legacy-dotnet-agent-kit

Then restart Codex so the new skill is picked up.

One-line install

Run:

curl -fsSL https://raw.githubusercontent.com/Mohrimn/legacy-dotnet-agent-kit/main/scripts/install-skill.sh | bash

The installer copies only the skill folder into:

${CODEX_HOME:-$HOME/.codex}/skills/legacy-dotnet-agent-kit

Use --force if you intentionally want to replace an existing local copy:

curl -fsSL https://raw.githubusercontent.com/Mohrimn/legacy-dotnet-agent-kit/main/scripts/install-skill.sh | bash -s -- --force

Manual install

Clone the repository and copy the skill folder:

git clone https://github.com/Mohrimn/legacy-dotnet-agent-kit.git
mkdir -p "${CODEX_HOME:-$HOME/.codex}/skills"
cp -R legacy-dotnet-agent-kit/skills/legacy-dotnet-agent-kit "${CODEX_HOME:-$HOME/.codex}/skills/"

Then restart Codex.

Quick start

After installation, ask your agent to use the skill for a specific task:

Use LegacyDotnetAgentKit to assess the Employee Review WPF module and produce a source-backed modernization slice plan.

Or, without installing it, copy or reference the skill folder from:

skills/legacy-dotnet-agent-kit/

For non-Codex workflows, start with these templates:

• templates/architecture-map.md
• templates/current-behavior-map.md
• templates/migration-risk-register.md
• templates/modernization-slice-plan.md
• templates/regression-test-matrix.md

Planned scanner

A future version may add a .NET tool or Roslyn analyzer package for mechanical checks such as:

• sync-over-async on UI paths
• fire-and-forget first-render data loads
• direct server calls from UI files
• legacy reporting dependencies
• suspicious cache calls that ignore request shape
• generic CRUD around domain records that appear to require purpose-specific operations

The scanner is intentionally deferred until the workflow and checklists are stable.

License

MIT. See LICENSE.