Legacy SoftwareModernization
Move an ageing system to a modern platform in controlled steps, keeping your data, your business rules and your daily operations intact.
Legacy Software Modernization: what the work involves
Legacy software is rarely bad software. It is a system that has quietly encoded years of business rules, running on a platform that is hard to hire for, hard to secure and impossible to reach from a phone. The original developer may be gone, the source may be incomplete, and every change is a risk. Yet a full rewrite is dangerous because nobody remembers exactly what the old system does. The craft is in recovering that knowledge before moving it.
DevKey starts with discovery: reading the code and database where available, interviewing users, and recording the rules the system actually enforces. We then choose a path, such as wrapping with an API, replacing module by module, or rebuilding with a parallel run, and migrate data with reconciliation at every stage. The old system stays available until the new one has matched its outputs, so users switch only when results agree.
Core features
Discovery and rule extraction
We document screens, reports, database structure and the business rules hidden in code, producing a map of what must be preserved.
Strategy options and trade-offs
Rehost, wrap, replace in phases or rebuild: we present each option with its risks and agree a path that fits your tolerance for change.
Incremental module replacement
Modules move one at a time behind a shared database or API, so the business never depends on a single risky cutover weekend.
Data migration with reconciliation
Records are cleaned, transformed and loaded in rehearsals, with totals and sample records compared to the old system until they agree.
Parallel run and cutover plan
Old and new run side by side on real transactions, outputs are compared, and a rollback plan is rehearsed before the final switch.
Documentation and knowledge transfer
The new system ships with architecture notes, data dictionary and runbooks, ending dependence on any one person's memory.
What we get right before launch
Missing or locked source code
Sometimes only the compiled program survives. We can still document behaviour from its database and screens and rebuild around outputs, though this takes longer and we say so up front.
Dirty historical data
Years of workarounds leave orphaned records and inconsistent codes. We budget time for cleaning and agree rules with you, instead of migrating problems into the new system.
User retraining
A faster system that confuses people fails. We keep familiar workflows where they work, change them where they do not, and train users before cutover rather than after.
Tools and technology
- Next.js
- React
- TypeScript
- Node.js
- PostgreSQL
- Prisma
- SQLite
- Docker
- REST
Common questions, answered
Do we have to rewrite everything at once?
No, and we usually advise against it. Replacing one module at a time, or placing an API in front of the old system first, lowers risk and lets you see benefits sooner while operations continue.
What if nobody has the source code?
We can still study the database, reports, screens and user behaviour to reconstruct the rules. This is slower and less certain than having the source, so we scope it carefully and test aggressively against real outputs.
Will we lose our historical data?
Not by design. Data is migrated in rehearsals with totals compared to the old system, and the old database is kept read-only for a defined period so anything questioned can be checked against it.
How do you avoid downtime?
By running old and new in parallel, migrating in stages and choosing a quiet window for the final switch, with a rehearsed rollback. The aim is that users notice improvement, not an outage.
More Custom Business Software services
All Custom Business Software servicesSystem Integration Services
Connect the systems you already run so that data is entered once, flows where it is needed and stays consistent everywhere.
Desktop Application Development
Installed software that opens fast, talks to local hardware and keeps working when the network does not.
API Development Services
Well-designed REST and GraphQL interfaces that let your apps, partners and systems share data reliably and securely.
Ready to start your Legacy Software Modernization project?
Tell us what you need and we will come back with a clear scope, timeline and the questions worth answering before any build starts.