Legacy modernization to Blazor or React
Take the old app apart before you rebuild it
Big-bang rewrites fail because nobody knows what the old app does. Agents separate every screen into its interface, its rules, and its data, then rebuild it in Blazor or React on Syncfusion components, one tested screen at a time.
YOU HAND OVER
YOU GETOrders screen in React14 rules kept · parity tests pass
Built by Syncfusion, serving 47,000+ organizations.25+ years of developer tools, now reimagined for the agent-first era.
47,000+Syncfusion customers
1,600+Syncfusion UI components
25+Years of Syncfusion developer tools
Rules before rewrites
Review legacy behavior with the business owner
The people who wrote the app moved on years ago. The rules didn’t. Each one is traced to the code that enforces it, so the business owner can confirm the logic before anything is rebuilt.
No switch-off day
Replace legacy screens one pull request at a time
Nobody wants a switch-off day. Each rebuilt screen arrives as its own pull request once its parity tests pass, so your team can release it while the old app keeps serving the rest.
Week 1 of 120% of traffic on the new app
Live in Blazor · 0 screensIn parity testingStill on WebForms
Share of daily traffic served by the new app, by week
Parity tests, per screen
Compare old and new screen behavior before merging
The same day, twice
Hannah checks behavior before replacing a legacy screen
Illustrative example, not a customer result.Here is what the work looks like today, and what changes when an AI team takes the busywork off the plate.
Without BoldCreate
With BoldCreate
With BoldCreateMon
The premium screen runs on WebForms. Nobody wants to touch it.Key-person risk
Agents map the screen: inputs, rules, and side effects.Behavior documented
Tue
A rewrite estimate comes back: 18 months.Rejected
Parity tests written against the old screen.124 checks
Wed
A small change takes four days because nobody understands it.4 days
New ASP.NET Core + React screen built behind a flag.Preview ready
Fri
The one engineer who knows it hands in notice.Knowledge leaving
Side-by-side run on real cases. Results identical.Parity checks passed
One legacy screen replaced with proven parity in a week
Frequently asked questions
How does legacy modernization work without a big-bang rewrite?
Agents map every screen and business rule in the old app, then rebuild it in Blazor or React on Syncfusion components. Each screen comes back as its own tested pull request while the old app keeps serving the rest.
How do I know a rebuilt screen behaves like the old one?
Each screen comes with parity tests that compare old and new behavior on the same inputs. Your team releases it only after they pass.
Who confirms the business rules before the rebuild?
Each rule is traced to the code that enforces it, so your business owner can confirm the logic before anything is rebuilt. The map, the rules, and the tests stay in your repository.
What do I need to start a modernization project?
Connect the legacy repository, choose Blazor or React, approve the screen inventory, and start with one screen.