VB.NET WinForms to SPA + .NET API Migration Playbook

Tell us what you're building

We use these answers to surface the prompts, skills, and MCP configs that fit your stack — and to substitute stack values like {{database}} into the prompts you copy. Content (PRDs, code, etc.) stays in your repo. Everything you enter here is stored in your browser — nothing is sent to a server.

Steps you'll go through

1. 01

   Audit the WinForms App

   2-3 weeks

   Inventory every form, local-resource dependency, and single-user assumption. WinForms apps hide a lot in code-behind and stored procs.

2. 02

   Reshape Architecture for Multi-User Web

   2-3 weeks

   Redesign the app for the web before migrating any code. The most important phase — get this wrong and you ship a desktop app rendered in a browser.

3. 03

   Map the Data Model

   2-3 weeks

   Plan how data moves from on-prem SQL Server to cloud-hosted DB, including any schema reshape and stored-procedure migration.

4. 04

   Design the API

   2-3 weeks

   Define the API contract before writing any backend code. Web realities (network latency, pagination, versioning) drive the design — not the WinForms patterns.

5. 05

   Design Authentication

   2 weeks

   Plan the move from Windows Authentication (typical for WinForms) to web auth (OAuth / JWT via an IdP).

6. 06

   Migrate Vertical Slice 1

   6-8 weeks

   Pick a small, contained workflow (e.g., "view customer details"). Build the entire vertical: SPA page → .NET API → DB query. Use it to validate every architectural decision.

7. 07

   Continue Migrating Slices

   2-4 quarters

   Migrate the remaining capabilities, refining patterns as you go. Edge cases (file uploads, printing, real-time data) emerge mid-way through this phase.

8. 08

   Pilot with a Subset of Users

   4-6 weeks

   Move 5-10% of users to the new app exclusively. Watch their behavior. Fix what breaks. This is where the workflows nobody mentioned (because they were "obvious") surface.

9. 09

   Cutover with Rollback Plan

   4-8 weeks

   Move the remaining 90% of users to the new app — usually a phased rollout over weeks, not a single cutover day.

10. 10

    Decommission the Desktop Installer

    2-3 weeks

    Remove the WinForms installer / ClickOnce deployment. Decommission the build pipeline. Archive code. Run the retro.