Migrate Legacy App to React — Without Re-launching Your Site
Old stack out, new stack in — without a re-launch
What you're seeing
Your internal app runs on AngularJS, Backbone, or vanilla JS, and adding features takes weeks.
Our approach
We re-architect on React + TypeScript with proper state management, ship features in parallel with the migration, and retire the legacy code safely.
Symptoms teams come to us with
- A legacy stack where every change is risky and slow
- Poor SEO and slow first paint from a client-only SPA
- Hiring is hard because nobody wants the old framework
- A big-bang rewrite has stalled or scares everyone
How we de-risk it
- 01Route-by-route strangler-fig migration, no big-bang launch
- 02SEO and data parity verified at every step
- 03Feature flags so old and new run side by side
- 04A clean decommissioning checklist for the old system
What you get
Concrete deliverables, no fluff
Every engagement ends with measurable, documented outcomes — no black-box agency reports.
Migration plan with route-by-route mapping
Incremental cut-over, no big-bang launch
Data + SEO parity verified at every step
Decommissioning checklist for the old system
From brief to shipped fix
A transparent, low-risk process — a senior engineer reads your brief personally, and nothing starts until you approve a written plan and price.
Diagnose
A senior engineer reviews your brief, reproduces the issue, and pinpoints the real root cause — not the symptom — before any code is touched.
Scoped plan & quote
You get a written plan to migrate Legacy App to React, a firm timeline, and a fixed quote. Nothing starts until you approve it — no surprise invoices.
Ship the fix
We implement on a branch and open a pull request you review, working to your code-review standards on your repo — never a black box.
Verify & hand off
We verify on staging and production, share before/after evidence where it applies, and leave you a short hand-off note so the fix sticks.
Why teams hand this task to Krapton
Senior engineers only
Your brief is read and handled by a senior engineer — no junior hand-off, no sales-rep filter in between.
Root cause, not a patch
We reproduce and fix the underlying cause, then add a guard so the same class of issue does not quietly return.
Your repo, your standards
Every change lands as a pull request you review, on your repository, following your existing review process.
NDA on day one
Confidentiality and IP are covered before we look at a single line of code. All work stays in your accounts.
Fixed quote up front
You approve a written plan and price before work starts. If scope changes, we re-quote in writing — no surprise invoices.
Proof, where it applies
Performance, SEO and reliability work ships with before/after evidence so the result is measurable, not anecdotal.
Three ways to engage
No retainer required. Pick the model that matches the work — pricing for this task starts from $3,500, with a fixed quote before anything starts.
Per task
Most popularOne clearly-scoped fix at a fixed price. Best when you know exactly what is broken and want it handled end to end.
- Fixed quote up front
- One PR, reviewed by you
- No retainer required
Hourly
Pay only for the hours worked. Best for diagnostics, audits, or exploratory work where the scope is still emerging.
- Weekly timesheets
- Pay for what you use
- No minimum commitment
Per sprint
A focused 1–2 week sprint when the work is bigger than one fix but smaller than a full project.
- 1–2 week blocks
- Clear sprint goal
- Scale up or stop anytime
Tooling we use
Industry-standard stack, no proprietary lock-in
Migrate Legacy App to React — your questions, answered
How much does it cost to migrate Legacy App to React?
Pricing starts from $3,500 and depends on the scope we find during the diagnostic. You get a fixed, written quote before any work begins — most engagements like this run 3–10 weeks.
How long does it take to migrate Legacy App to React?
Typically 3–10 weeks for a focused engagement. After a short diagnostic we commit to a firm timeline so you know exactly what to expect.
Will you work directly on our existing codebase?
Yes. We work on your GitHub, GitLab or Bitbucket, ship every change as a pull request you review, and follow your code-review standards — not ours.
What exactly will I have at the end?
Concrete, documented outcomes — Migration plan with route-by-route mapping, Incremental cut-over, no big-bang launch, Data + SEO parity verified at every step, and more. No black-box agency report.
How quickly can you start, and do you sign an NDA?
For a focused task like this we can usually start within 24–48 hours of the brief. We sign an NDA on day one, before we look at any code — yours or ours.
Can you migrate without taking the site offline?
Yes. We migrate route-by-route with the strangler-fig pattern, running old and new side by side behind feature flags, with SEO and data parity checked at every step — no big-bang cutover, no downtime.
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Let's get this off your plate
Send a 60-second brief on Migrate Legacy App to React and a senior engineer replies within 24 hours with a plan and a fixed quote. NDA on day one, no retainer required.