Do we have to freeze or shut down the old app during the rebuild?

No. The rebuild uses a staged, strangler-fig approach: the legacy system keeps running and serving real users while the new one is built and proven feature by feature. Traffic moves over in slices, with the old system as a live fallback, so there's never a freeze or a big-bang switchover.

How do you avoid a risky big-bang rewrite?

By never doing one. Each feature is rebuilt, shadowed against the old system to check parity, and cut over on its own — so risk is always contained to a single slice, not the whole app. If a slice isn't right, the old path is still there to fall back to while we fix it.

What happens to our existing data?

It's migrated with validation and reconciliation as part of the build. We move records into the new schema, check them against the old system, and make sure the totals tie out before a feature depends on them — so the migration is proven, not hoped.

The original developer is gone and there are no docs. Is that a problem?

That's the normal starting point for a legacy rebuild. Part of the early work is mapping what the app actually does by reading the code and watching real behaviour, rather than trusting missing or stale docs. A senior engineer inheriting an undocumented system is exactly what this build is for.

How long does a legacy rebuild take?

Most take eight to twelve weeks, depending on how much the app does and how tangled the data is. It runs on the flat monthly subscription — with multiple plans available — so you pay for the active weeks rather than a fixed total, can pause between slices, and keep the old system running the entire time.

What do your legacy application modernization services actually cover?

The end-to-end rebuild: mapping what the legacy app does, standing up a supported stack, a strangler-fig routing layer so old and new run side by side, feature-by-feature cutover with parity checks, data migration with reconciliation, and a documented handover. It's application modernization delivered as a staged build, not a one-off audit or a lift-and-shift.

Should we repair the legacy app instead of rebuilding it?

Sometimes, and we'll say so. If the app is stable and only needs a framework bump, a dependency upgrade, or a contained fix, a full rebuild is overkill — the honest answer is repair, not rebuild. We map what's actually failing first and only recommend modernization for the parts that warrant it, so you're not paying to rewrite code that already works.

Engagements - Legacy app modernization: a staged, tested rebuild — not a big-bang rewrite

The legacy app still runs the business, but every change is terrifying, the original dev is long gone, and the framework's been out of support for years. You can't freeze it and you can't keep patching it. A rebuild does it the safe way: the new system gets built and proven feature by feature while the old one keeps running, and traffic moves over in stages — no big-bang rewrite, no weekend where everything's supposed to just work.

Start next week8–12 weeks typical

Teams stuck on legacy
Post-acquisition cleanups
Agencies

What you'll have at launch

A modern app on a maintainable stack, cut over in stages — the old system live until the new one is proven, no big-bang rewrite.

A modern app on Next.js and PostgreSQL replacing the unmaintainable stack, feature-for-feature where it counts.
A staged cutover: the old system stays live as a fallback until each slice of the new one is proven in production.
The data migrated and reconciled, so nothing's lost and the numbers still add up after the move.
A codebase your team can actually change without holding its breath.

How we build it

A build runs 8–12 weeks typical, shipped week by week in increments you review and merge.

Weeks 1–3 · Map & strangle

We map what the legacy app actually does (not what the docs claim), stand up the new stack, and put a routing layer in front so new and old can run side by side. The first slice gets rebuilt and shadowed against the old system to prove parity before anything real moves.

Weeks 4–9 · Rebuild feature by feature

Features get rebuilt and cut over in priority order, shipping weekly. Each slice runs against real traffic with the old system still available as a fallback, and the data migration is validated as we go — so risk stays contained to one feature at a time, never the whole app at once.

Weeks 10–12 · Final cutover & decommission

The last features move, the data migration is reconciled end to end, and once the new system's proven we retire the legacy app. You end on a modern, tested codebase with the old one gone — not two systems you now have to maintain.

What's included

A strangler-fig migration: a routing layer so the new app and legacy system run side by side, with traffic moved feature by feature.
A rebuild on Next.js and PostgreSQL (or the right modern stack for your case), matched to how the business actually uses the app.
Data migration with validation and reconciliation, so records move cleanly and the numbers still tie out afterward.
Parity checks: new features shadowed against the old system before cutover, so you're not discovering gaps in production.
A staged rollout with the old system as a live fallback, so no single change can take the whole business down.
Deploy, backups, and a documented handover, so the modern app is genuinely yours to run and change.

What a build like this looks like

Scopes we've shaped this engagement around. Yours is one of them, or close enough that week one settles it.

The framework's been out of support for years. The app runs on a version nobody patches anymore, and security updates stopped shipping. Legacy application modernization rebuilds it on a supported stack feature by feature, so you move off the dead framework without a freeze — the old system keeps serving users until each modernized slice is proven.
The original developer is long gone, and so are the docs. Nobody left understands how it works, and every change is a guess. The rebuild starts by mapping what the app actually does from the code and real behaviour, then modernizes it in reviewed increments — so the knowledge ends up in a codebase your team can read, not in one person's head.
Every change is terrifying because there are no tests. One fix breaks three things you didn't touch. The modernization builds a parity test harness as it goes: each feature is shadowed against the old system before cutover, so the rebuilt app ships with the safety net the legacy one never had.
Data migration and cutover are the scary part. Years of records live in a schema you can't risk corrupting. The build migrates data with validation and reconciliation, running shadow reads against the old system until the numbers tie out — so cutover is a proven step, not a weekend everyone dreads.

Stack

Next.js
PostgreSQL
Docker
VPS

How this build lowers your risk

Repair vs rebuild, decided honestly. Not every legacy app needs a full rebuild — sometimes the right move is a targeted upgrade, a framework bump, or leaving a stable core alone. Early on we map what's actually failing and tell you which parts to modernize and which to keep, so you're spending the build on the app that warrants it, not rewriting code that works.
No big-bang rewrite, ever. The strangler-fig approach means the new system is built and cut over one feature at a time, with a routing layer keeping old and new side by side. Risk stays contained to a single slice — never the whole app on one launch day — and the old path is always there to fall back to.
Parity proven before anything real moves. Each rebuilt feature is shadowed against the legacy system and checked for parity before it takes real traffic, so you're not discovering behaviour gaps in production. The modernization ships as reviewed PRs into your repo with tests on the paths that matter.
The old system stays live as your rollback. Until a modernized slice is proven, the legacy app keeps running as a live fallback. If a cutover isn't right, traffic routes back to the old path while we fix it — so no single change can take the business down, and you're never trapped mid-migration.

Is this the right build for you?

A good fit when

A legacy app still runs the business but is on an unsupported framework, hard to change, or lost its original developer.
You want a staged, tested modernization — the old system live the whole time — not a risky big-bang rewrite.
Data migration and cutover risk are real, and you need parity checks and reconciliation, not a hope-it-works switchover.
You want one senior engineer owning the rebuild over a month or more, shipping weekly increments you review and merge.

Not a fit when

The app is stable and only needs a small fix or dependency bump — that's a task, and often the honest answer is don't rebuild.
You want a same-day bug fix or a single feature patched — that's one-off work, not a month-plus modernization build.
There's no working system yet; a SaaS MVP build comes before a rebuild.
You want a lift-and-shift hosting move with zero code changes rather than an actual application modernization.

Scope your build Compare every build

How it runs on the subscription

A rebuild is the definition of month+ work — staged, validated, feature by feature — so it runs as a build: the board dedicated to modernizing your app, cutting over a slice every week. We match the monthly plan to the workload, with most rebuilds landing in eight to twelve weeks. Because it's staged you reprioritize which feature moves next and pause between slices, with the old system live the whole time as your safety net.

Frequently asked questions

Do we have to freeze or shut down the old app during the rebuild?: No. The rebuild uses a staged, strangler-fig approach: the legacy system keeps running and serving real users while the new one is built and proven feature by feature. Traffic moves over in slices, with the old system as a live fallback, so there's never a freeze or a big-bang switchover.
How do you avoid a risky big-bang rewrite?: By never doing one. Each feature is rebuilt, shadowed against the old system to check parity, and cut over on its own — so risk is always contained to a single slice, not the whole app. If a slice isn't right, the old path is still there to fall back to while we fix it.
What happens to our existing data?: It's migrated with validation and reconciliation as part of the build. We move records into the new schema, check them against the old system, and make sure the totals tie out before a feature depends on them — so the migration is proven, not hoped.
The original developer is gone and there are no docs. Is that a problem?: That's the normal starting point for a legacy rebuild. Part of the early work is mapping what the app actually does by reading the code and watching real behaviour, rather than trusting missing or stale docs. A senior engineer inheriting an undocumented system is exactly what this build is for.
How long does a legacy rebuild take?: Most take eight to twelve weeks, depending on how much the app does and how tangled the data is. It runs on the flat monthly subscription — with multiple plans available — so you pay for the active weeks rather than a fixed total, can pause between slices, and keep the old system running the entire time.
What do your legacy application modernization services actually cover?: The end-to-end rebuild: mapping what the legacy app does, standing up a supported stack, a strangler-fig routing layer so old and new run side by side, feature-by-feature cutover with parity checks, data migration with reconciliation, and a documented handover. It's application modernization delivered as a staged build, not a one-off audit or a lift-and-shift.
Should we repair the legacy app instead of rebuilding it?: Sometimes, and we'll say so. If the app is stable and only needs a framework bump, a dependency upgrade, or a contained fix, a full rebuild is overkill — the honest answer is repair, not rebuild. We map what's actually failing first and only recommend modernization for the parts that warrant it, so you're not paying to rewrite code that already works.

Related builds and services

Got a project? Let's ship it.

3 spots open. Tell us what you need shipped. We’ll match the plan and timeline to the work on a short sales call, then deliver it in reviewable increments.

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