01
Route manifest
One line per page decides which app answers it. Patterns are supported, so a whole template family flips as one group instead of page by page.
Legacy application modernization services
Modernize the system one route at a time. Every step live in production, every step reversible.
Every release on an aging stack is a risk, and fewer engineers want to work on it. We move .NET Framework to .NET 8, Java 8 monoliths to Java 21, AngularJS and WebForms to React and VB6, Delphi and WinForms systems forward in packages that ship one at a time, while the old system keeps serving everything not migrated yet.
- The new app becomes the front door. Migrated routes are served by the new stack, everything else is proxied to the legacy app unchanged. Same domain, no redirects, sessions intact.
- One line switches a page over, and back. A route manifest decides per page which app answers, so a rollback is the same line reversed.
- The legacy app needs zero code changes for any of this, and it is retired only when the manifest no longer points to it.
- Work is contracted in capped packages of 1 to 3 weeks. You pay actual effort up to the cap, never above it, and you can pause at any package boundary with everything working.
5.0Clutch rating, 45 reviews
100+certified engineers
98%client recommendation rate
2018founded
Results from Devox modernization projects
Faster, safer migrations, measured on live systems
Zerodowntime during the cloud migrationUS EdTech, more than half a million active users
3 weeksof migration planning instead of 10Logistics platform, AI-assisted discovery
−40%shorter migration cycleAI-based dependency analysis
<5 minmean time to recoveryAI-assisted rollback triggers
The architecture we use
The new app becomes the front door. Everything else passes through untouched.
Two apps run in parallel behind one domain. Migrated routes are served as real pre-rendered pages; everything else hits a catch-all that proxies the request unchanged to the legacy app. Same domain, no redirects, cookies intact.
02
Middleware router
Checks the manifest on every request: migrated pages are served by the new app, everything else is proxied to the legacy one. Optionally driven by an environment variable, so a flip needs no deploy at all.
03
Shared session and data bridges
The user token moves into a domain-scoped cookie both apps read, so a login on either side is valid on both. Temporary bridges keep shared state, such as a cart, in exactly the format the legacy app expects, and are deleted once that flow migrates.
04
Business logic extracted once
Framework-free pricing, discount and calculation code becomes a shared package imported by the new app and loaded by the legacy one exactly as before. One source of truth, covered by a parity test suite that proves both produce identical results.
The route manifest, in practice
"/pricing" : "next" // migrated, served by the new stack "/catalog/*" : "next" // a whole template family, flipped as one group "/checkout" : "legacy" // still served by the old app, untouched
Flipping a page is one line and a deploy, roughly two minutes. Rolling it back is the same line reversed.
Two ways to modernize
A full rewrite asks you to bet the business on a launch date
Both routes end at the same modern stack. They differ in what happens between the decision and the finish line.
Big-bang rewrite
Everything moves on one date
- ✕Nothing is usable until the whole system is finished.
- ✕The feature freeze lasts for the length of the rewrite.
- ✕Rollback means going back to the old system entirely.
- ✕The estimate is a guess made before anyone has worked in the code.
- ✕Padding for uncertainty is baked into the number on day one, and it stays with the vendor.
Staged migration, Devox
One route at a time, always reversible
- ✓The first real page is live in production inside the first package.
- ✓The legacy app keeps serving everything not migrated yet, with zero code changes.
- ✓Rollback is one line in the manifest, not a project.
- ✓Each package is priced from the pace measured on your actual code, so every following quote tightens.
- ✓Each package ships complete, so you can pause at any boundary with everything working.
See which path fits your system 30 minutes on Zoom, no cost
The first package
A two-week foundation stage that ends with something live
Everything after it runs on this machinery, and it produces the plan and the estimates for the next packages from your actual code rather than from assumptions.
Week 1
Audit and estimation plan
A solution architect goes through the codebase with your developer in a walkthrough session, then writes the plan and the estimates for the following milestones.
You provide: repository and environment access, and same-day answers on legacy behavior.
Week 1–2
Switching machinery
New project and CI, front-door routing with per-page switching in both directions, deployment pipeline, domains and SSL, rollback path, shared login session across both apps.
Roles: senior engineer and DevOps, with a PM as your single point of contact.
End of week 2
First real page live, and back
Business logic extracted into a shared package, a test suite proving identical results, and one real page switched live in production, then switched back to prove the rollback path.
You get: a live page on your domain, reversible with one change, plus the estimation plan.
How the work is contracted
Capped packages instead of one padded number
Work is contracted in short packages of one to three weeks. A larger milestone spans several of them.
Capped work packages
- ✓Each cap is your worst case. You pay actual effort up to it, never above.
- ✓When the work outruns the estimate, the package closes under cap and you keep the difference.
- ✓The next package is priced from the real pace measured on your code, so proven speed makes every following quote cheaper.
- ✓Each package ships complete and reversible, so you can pause at any boundary with everything working.
One fixed price for the whole rewrite
- ✕Padding for uncertainty is baked into the number on day one.
- ✕When tooling gets faster, that padding stays with the vendor and the gains never reach your invoice.
- ✕No risk above the cap and all upside below it is exactly what this shape cannot offer.
- ✕Pausing mid-way leaves you with a half-migrated system and no working boundary to stop at.
Three things are decided after the foundation stage rather than guessed now: whether flips go through a deploy or an environment variable with no deploy at all, how the most complex module is split between our engineers and yours, and the estimates for the remaining milestones, planned out during the audit from your actual codebase.
AI acceleration, per task
Measured per task, with a named human checkpoint on each one
Blanket discounts on AI do not survive contact with a real migration. Measured reality is uneven: overall project gains land around 10 to 30 percent even with near-universal tool adoption, while specific task types genuinely run twice as fast.
| Work type | AI impact | What the human keeps |
|---|---|---|
| Type definitions, scaffolding, configuration | 60–80% faster | Correctness review |
| Converting framework-free business logic | 70–90% faster | Parity test sign-off |
| Simple and static pages | 50–60% faster | Visual QA |
| Template sections and UI components | 40–50% faster | Design fidelity and accessibility |
| Checkout, cart and other complex flows | ~30% faster | Business-logic validation |
| Verifying the live system behaves identically | ~0% | All of it |
Why the total does not drop by 70 percent: those percentages apply to writing code. Every migrated page still needs an engineer to review the output, compare it against the live system, test real user flows, deploy, flip and watch it. The published cases where AI rewrote a system in days all had one thing in common, an existing test suite complete enough to judge every change automatically. Where that automatic verdict exists, AI genuinely runs at twice the pace. Where the verdict is a human looking at a live system, verification sets the clock. That is why the foundation stage builds a parity test suite for the money-critical logic first.
How we keep production safe
Designed like a critical infrastructure project
Sandbox first
Every phase starts with sandbox testing and validation in parallel environments.
Then: changes go out incrementally once the system is stable.Dependencies mapped
Business-critical workflows and dependency chains are mapped with static and dynamic analysis before anything migrates.
Then: the migration order follows the map, not the org chart.Rollback on every wave
Clear rollback points, database diff checks, contract testing, feature flags and blue-green delivery.
Then: a bad flip is reversed in minutes, not in a release cycle.Money-critical logic parity-tested
Pricing, discount and order calculations must produce identical results in both implementations. Any divergence would show up as billing discrepancies.
Then: both run in parallel during QA until the results match.
Technology
The stack we migrate from, and the stack we migrate to
Age alone does not decide the approach. Framework support status, test coverage, the hiring market for the stack and release frequency do, and the assessment scores these before any code is touched.
Legacy systems we take over
.NET Framework 4.xWebFormsASP.NET MVCClassic ASPVB6DelphiWinFormsJava 8 monolithsAngularJS 1.xPHP 5Mainframe workloadsOn-premise application servers
Back end we migrate to
.NET 8 / .NET 10C#Java 21Spring BootNode.jsExpressPythonFastAPIREST and GraphQL APIsModular monolithMicroservices where teams need autonomy
Front end
ReactNext.jsTypeScriptServer-side renderingStatic generationZustandReact Hook FormZodDesign system and component library
Data
PostgreSQLMicrosoft SQL ServerMySQLMongoDBRedisSchema and data migration toolingDatabase diff checks
Cloud and delivery
AWSAzureGoogle CloudDockerKubernetesCI/CD pipelinesBlue-green deliveryFeature flagsInfrastructure as codeObservability and alerting
Quality and safety net
Parity test suitesContract testingRegression automationStatic and dynamic dependency analysisLoad and stress testingSecurity scanningAccessibility review
Server-side rendering and static generation are chosen per route rather than for the whole application: public pages are pre-built and served as full HTML, which is what search engines and AI crawlers need, while personal pages such as cart and account stay dynamic because crawlers do not index them. Third-party prerendering services can be retired page by page as routes move over.
Case studies
Legacy systems that kept running while they changed
Zero-downtime cloud migration with AI-assisted rollback
Thousands of live exam sessions ran daily while dozens of interconnected applications moved to the cloud.
- Zerodowntime: platform uptime maintained through the entire migration window
- 30% → 95%documentation coverage, auto-generated
- −60%post-migration support incidents
AI-powered dependency mapping and migration planning
Three disconnected systems with limited documentation and workflows too critical to interrupt.
- 3 vs 10weeks of planning instead of the manual estimate
- −70%migration planning time
- 45–55%faster discovery
FAQ
What CTOs ask before they start
Will the migration disrupt ongoing operations?
Nothing moves without simulation, rollback protocols and real-time observability. Every phase starts with sandbox testing in parallel environments, and a migrated route goes live only after it is proven, with the manifest entry ready to be reversed.
Do we have to change the legacy application?
No. The legacy app keeps running unchanged behind the front door and keeps serving every route that has not migrated. It is retired only when the manifest no longer points to it, at which point the proxy and the temporary bridges are deleted.
What happens if a migrated page misbehaves in production?
The route goes back to the legacy app with one line in the manifest and a deploy of roughly two minutes, or with no deploy at all if flips are driven by an environment variable. That decision is made during the foundation stage, with knowledge of your pipeline.
How do you make sure pricing and calculations stay identical?
Framework-free business logic is extracted into a shared package that both applications use, and a parity test suite proves both produce identical results. Both implementations run in parallel during QA to catch any divergence before it reaches an invoice.
We are migrating applications to the cloud at the same time. Does that change anything?
No, it fits the same shape. Migrating legacy applications to the cloud happens per route as well: a migrated route can already run on the new infrastructure while the rest of the system stays where it is, and the manifest decides which one answers. Lift-and-shift, re-platforming and re-architecting are chosen per component, not for the whole estate at once.
Can we pause the project?
Yes. Each package ships complete and reversible, so you can stop at any package boundary with the system fully working, and resume later without unwinding anything.
Do we have to rewrite everything?
No. The choice is made per application: refactor when the code still holds business value, rebuild when the framework is dead, replace when the function is a commodity, retain when nothing is gained by touching it. Staged modernization ships value from the first package.
How quickly will we see a return?
Companies typically notice tangible financial and operational benefits within 3 to 6 months of beginning modernization, such as lower infrastructure costs, better application performance and reduced maintenance costs.
How much retraining will our team need?
We choose tools that build on your team's current skills, and provide hands-on training, clear documentation and knowledge transfer as part of delivery.
Find out what your modernization would take
30 minutes on your stack and constraints: which path fits, what the first two-week package would deliver, and what has to be true before anything is switched over.
Pick a time Free call on Zoom