Automation and Integrations
Replace an aging system step by step, without stopping the business
Big-bang rewrites of business-critical systems often fail. We modernize in small, safe steps: new parts take over one by one while the old system keeps running.
The problem
The problem this solves
Many businesses depend on a system built ten or twenty years ago. It works, and it encodes years of business rules and exceptions. But it is written in a technology few developers know, hosted on aging servers, hard to connect to anything new and risky to change. Every year the technical debt grows and the people who understand it get harder to find.
The obvious answer, a complete rewrite, is the riskiest. Rewrites take longer than planned, miss business rules nobody remembered, and ask the business to switch everything on one day. Many are abandoned halfway, leaving two systems to maintain.
We use a gradual approach, often called the strangler pattern. First we capture how the current system behaves with characterization tests, sometimes called golden-master tests, so we can prove the new parts do the same thing. Then we build new components around the old system, route one feature at a time to the new code, and keep data in sync, often one way at first, until the old part can be switched off.
AI has made this much more practical. It can read and summarize large, old codebases quickly, explain undocumented business rules, generate characterization tests and draft migration plans. People still decide what to keep, what to change and when each switch happens.
This is exactly the approach described in our beach rental booking system case study, where a long-running booking system had to keep taking bookings while a modern stack was planned alongside it.
What you get
What you get
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System analysis
Code, data, integrations and business rules documented, many for the first time.
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Characterization tests
Tests that capture current behavior so changes can be proven safe.
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Modernization roadmap
The order in which parts are replaced, with risks and milestones.
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Routing layer
A layer that sends each feature to old or new code, switchable per feature.
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Data sync
Sync between old and new databases while both are in use.
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New components
Modern replacements for each part, built with tests and documentation.
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New integrations
APIs so the business can finally connect the system to modern tools.
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Decommissioning
A safe shutdown of old parts once the new ones have proven themselves.
How we build it
How we build it
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1
Understand
AI-assisted reading of the codebase, plus interviews with the people who use it.
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2
Protect
Characterization tests written around the most important behavior.
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3
Plan
A roadmap that starts with the part that gives the most value or risk reduction.
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4
Replace piece by piece
Each part rebuilt, tested against the old one and switched over.
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5
Retire
Old parts switched off once nothing depends on them.
AI and people
Where AI helps, where people decide
AI makes the repetitive parts faster. The decisions that shape your product stay with experienced people.
Where AI speeds things up
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Reading and summarizing large legacy codebases.
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Explaining undocumented business rules.
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Generating characterization tests from real behavior.
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Drafting migration scripts and data sync code.
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Producing documentation of the old and new systems.
Where people decide
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Which parts to replace first, and which to keep.
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Which old rules are still correct, and which are bugs.
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The target architecture and technology.
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When each switch is safe.
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When the old system can finally be turned off.
Is this right for you?
When this is the right choice
A good fit when
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A critical system is hard to change, host or hire for.
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You cannot afford for the business to stop during a replacement.
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Business rules live in code nobody fully understands.
Consider something else when
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The system is small and a clean rebuild is low risk.
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An off-the-shelf product can replace it with little customization.
Timeline and cost
What affects the timeline and cost
Modernization is measured in months, delivered in steps that each bring value. The first new component and the safety net of tests usually arrive within the first few milestones.
We do not publish fixed prices because scope drives cost. How we estimate.
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System size
More features and code mean more to analyze and replace.
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Documentation
Undocumented systems need more investigation.
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Data complexity
Complex or inconsistent data makes sync and migration harder.
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Integrations
Systems that depend on the old one must be moved carefully.
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Uptime needs
No downtime allowed means more parallel running.
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Business involvement
Rules must be confirmed with the people who know them.
Keep exploring
Related services, solutions and reading
Related services
View all related services- Automation and Integrations CRM, payment and API integrations, MCP connections and workflows that stop people copying data by hand.
- Data migration Move data from an old system to a new one, cleaned, checked and without losing a record.
- Web applications Custom browser-based software for the work your team does every day, from booking tools to operations systems.
- API development Well-documented APIs that let your product talk to apps, partners and AI tools reliably.
- Internal tools Custom software for your own team: trackers, approval flows and back-office systems that replace spreadsheets.
- MVP development A first version with just enough features to put in front of real users and learn what to build next.
Solutions
View all solutions- AI automation and integrations Connect the tools you already use so data moves once, correctly, and AI reads the parts that arrive as text or documents.
- Approval workflows Requests, approvals and reminders in one place, with clear owners and deadlines instead of long email threads.
- Payroll automation Turn pay rules, attendance and leave into tested software so the monthly run becomes a review and payslips go out in one batch.
- Forecasting dashboards Forecast demand from your sales history and seasonality, and flag items to reorder before they run out.
- Email triage Sort a shared inbox by topic and urgency, pull out the key details and draft replies for a person to send.
Industries
View all industries- Vacation rentals Booking websites, owner and guest portals, turnover scheduling and guest messaging for rental operators.
- Manufacturing Quality inspection, production dashboards, quoting tools, knowledge assistants and legacy system modernization for manufacturers.
- Insurance Claims intake, document and photo processing, policy knowledge assistants and customer portals for brokers and insurers.
- Property management Tenant portals, maintenance tracking, owner statements and inbox automation for property managers.
Case studies
View all case studies- Beach rental booking system A long-running booking system kept earning while it was extended, tested and given a safe, gradual path to a modern stack.
- Vacation rental operations system One calendar per property, cleaning tasks created from bookings, and owner statements built from the same records.
- Facility management platform Every request, inspection and cost for every building now lives in one place, with a clear owner and status.
- Fashion deal aggregator Sale items from more than thirty brands are collected every night and classified consistently by a three-stage pipeline.
Guides and articles
View all guides and articles- How to migrate a legacy application Replace an old system step by step without stopping the business, with tests, data checks and a way back.
- How much does it cost to build a web app? What drives the cost of a web app, how complexity changes the budget, and how to keep spending under control.
- How to choose a development partner What to look for in a software development partner, the warning signs, and how to compare proposals fairly.
- Questions to ask before hiring a software agency Twenty questions that reveal how an agency works, who owns what, and whether they are the right fit.
- How AI changes software development cost Which parts of a software budget AI reduces, which it does not, and how to read an AI-assisted estimate.
- AI-accelerated vs traditional development How AI-assisted teams differ from traditional teams in speed, cost, quality control and risk.
AI models
View all ai models- Coding Models that write, review and explain code, and power coding assistants and developer tools.
- Mistral Medium 3.5 A newer open-weight Mistral model for agent and coding work, with image input, tool calling, structured outputs and a 256K window.
- GPT-6 Sol The middle model of the GPT-6 family, positioned for complex coding and agentic workflows at a mid price level.
MCP servers
View all mcp servers- Developer tools Servers for code hosting, version control, files, containers, error tracking and documentation lookup.
- Airtable Airtable's official hosted MCP server lets AI list workspaces, create bases and read records, with wider read and write access to tables and automations.
- Docker A community MCP server that lets AI list, run, stop and remove Docker containers and manage images, networks and volumes.
- Azure Microsoft's Azure MCP server lets AI work with many Azure services, from storage and Key Vault to SQL, monitoring and AKS, with a read-only mode.
- Context7 Upstash's Context7 MCP server gives coding assistants current, version-specific documentation for thousands of libraries.
- Everything The MCP project's Everything server is a test server that shows every protocol feature. For building and testing MCP clients only.
Glossary terms
View all glossary terms- Technical debt Technical debt is the future cost of shortcuts taken in software, such as quick fixes or missing tests, which make later changes slower and riskier.
- Database A database is an organized store of data that software can search, update and keep consistent, such as customers, orders or bookings.
- API An API, or application programming interface, is a defined way for one piece of software to request data or actions from another.
- Backend The backend is the part of an application that runs on servers, storing data, applying business rules and serving the frontend through APIs.
- API integration An API integration connects two or more systems through their APIs so data and actions flow between them automatically.
- Automation Automation is using software to perform a task or process with little or no human effort each time it runs.
FAQ
Questions about legacy modernization
Have a question that is not here? Ask us directly.
Full rewrites are risky: they take longer than planned, miss hidden rules and force a single high-stakes switch. Step-by-step replacement delivers value sooner and keeps the business running.
Yes. We read and maintain older stacks while planning the move to a modern one, and AI helps us understand unfamiliar code quickly.
With characterization tests that record what the old system does, which the new code must match, plus side-by-side comparison on real data.
See our guide how to migrate a legacy application and our data migration service.