How to reduce the risks of legacy system modernisation
Many companies rely on a legacy system that nobody is particularly eager to touch. Critical business processes depend on it, only a handful of people fully understand how it works, and every major change raises the same question: what might break?
Legacy system modernisation is often considered several times before a decision is finally made. The true scope of the project can be difficult to estimate, the system may have many dependencies, and nobody wants to risk disrupting day-to-day operations. There is also another important question beyond the technical side: what happens if the new system is delivered, but people continue working in exactly the same way as before?
Modernising a legacy system is therefore not just a technical project. One of the best ways to reduce risk is to understand both the existing system and the way people actually use it before development begins.
1. Start by understanding the current situation, not by building
One of the biggest risks in legacy modernisation is uncertainty. Documentation may be incomplete or outdated, new integrations and exceptions may have been added over the years, and some of the people who originally built the system may no longer work for the organisation.
Without a clear overall picture, it is difficult to estimate the workload, budget or the wider impact of a particular change. Before making major decisions, it is worth mapping at least three things:
- how the system works technically;
- which other systems and business processes depend on it;
- how people actually use it in their day-to-day work.
The better you understand the starting point, the fewer decisions you will need to make based on assumptions later in the project.
2. Look at both the code and the way people work
To build a complete picture of an existing system, you need two perspectives: the technical view and the user view.
AI-assisted code analysis can help teams understand a large codebase more quickly and map areas such as system architecture, business logic, integrations and dependencies. It can also help identify areas that require closer attention from a specialist. However AI does not decide how the system should be rebuilt, but it can help the technical team reach the right ideas faster.
For example, code analysis can help identify:
- which parts of the system depend on each other;
- which integrations are business-critical;
- where a change in one area could affect other functionality;
- which parts of the system require deeper analysis before changes are made.
The second perspective comes from the people who use the system. Code can show what a system does, but it does not always show how or why people use it.
For example, the code may not explain why an employee exports data to Excel every morning, why a customer service agent checks the same information in two different systems, or why a particular feature is used only once a year but becomes critical when it is needed.
This kind of knowledge often exists in people's heads rather than in the documentation. That is why it is important to talk to the employees who use the system every day and observe how the work actually happens. Only by combining the technical and user perspectives can you begin to decide what should be retained, what should change and what does not need to be carried over into the new system.
3. Do not build a new system as a copy of the old one
A common risk in legacy modernisation is simply rebuilding the old system using newer technology. This may feel like the safer option, but it can also carry years of unnecessary steps, exceptions and limitations into the new solution.
The opposite can happen too. A new system may be designed around the assumptions of management or the project team while overlooking how people actually work.
In both cases, the result can be a technically sound system that still sits alongside the same Excel spreadsheets, manual checks and old workarounds.
Before designing the new solution, it is worth reviewing existing workflows together with users. Which processes already work well? Which problems are caused by the system itself, and which come from the way work is organised?
It is also important to distinguish between exceptions that are genuinely necessary and those that have simply become habits over time.
The goal of a new system should not be to reproduce the old one as accurately as possible. It should support the work the organisation actually needs to do better.
4. Bring business and IT to the same table
Different stakeholders often see very different problems in a legacy system. IT may focus on technical debt, integrations, security risks and maintainability. The business side may see slow processes, manual work and missing functionality that employees need every day.
Both perspectives matter. Risk increases when technical and business decisions are made separately.
At the beginning of the project, business and IT should agree on the problems the modernisation is expected to solve, which processes are most critical, and how success will be measured once the new solution is in use.
It is equally important to agree on who has the authority to make key decisions when technical and business priorities conflict.
The clearer these agreements are from the start, the less likely it is that the project ends up with a technically sensible solution that does not meet the business need, or vice versa.
5. Measure more than whether the system was delivered
Launching a new system does not automatically mean the modernisation was successful. A few months after launch, it is worth looking at whether the new system has actually reduced the use of Excel spreadsheets, duplicate data entry and manual checks, and whether people are using the new workflow as intended.
These measures can often tell you more about the real outcome of the project than whether development was completed on the originally planned date.
The goal of legacy modernisation is not simply to introduce newer technology. It is to create a system that supports the organisation's work better than the old one did.
The first step does not have to be a large development project
You do not need to know the full scope of the project or the final budget before deciding whether to modernise a legacy system. At Trinidad Wiseman, we start the legacy modernisation process with a free three-hour workshop involving management and key users. Together, we review the current situation, identify the main risks and map the questions that should be answered before larger decisions are made.
From there, we can move on to a five-day assessment. During this stage, we use AI to analyse the system's code and technical structure while also speaking with the people who use the system every day and understand its business context.
By the end of the five days, you have an initial overall picture of:
- what the system currently does;
- the main technical and business risks;
- which questions still require further investigation;
- where it would make the most sense to begin the modernisation.
The findings and knowledge gathered during the assessment are yours to keep, regardless of whether you decide to continue the project with us.
Clarity before a major investment
If you’re considering modernising a legacy system but are not yet sure where to begin, get in touch. We’ll review your current situation, the main risks and the most sensible next steps together.
