Andreas
CEO & Founding Partner
from Belgium 🇧🇪
Legacy code modernization: how to evolve your SaaS without a risky rewrite
Are you a SaaS founder or CTO wrestling with a tangled, aging codebase? If your team is delivering updates at a snail's pace or dreading every deployment, you're likely dealing with legacy code.
Many tech leaders in your shoes consider a full software rewrite as a silver bullet. It's tempting to think "Let's start from scratch and do it right this time." But for 95% of situations, a ground-up rewrite is not the optimal path.
In this guide, we'll explore what legacy code really is, why "burn it down and rebuild" is often a dangerous gamble, and how you can modernize incrementally to save time, money, and morale.
Along the way, we'll show how madewithlove's seasoned CTO in residence and senior engineers can help turn your legacy system from a liability into a competitive advantage.
TL;DR: You don't have to risk everything on a Big Bang rewrite. By embracing your legacy code and improving it step by step, you can deliver value faster, reduce technical debt, and keep users happy – all while avoiding the common pitfalls of starting over. (And if you need expert help, you can book a call with us to discuss your legacy code challenges one-on-one.)
Legacy code modernization
It's more common than you think
"Legacy code" often gets a bad rap. It's the code everyone loves to complain about: outdated, messy, hard to maintain. A classic (tongue-in-cheek) definition is "legacy code is code without tests." Lack of automated tests does make code risky to change.
But legacy code isn't just about age or testing. In reality, any code in production is legacy code the moment it's deployed. Legacy code is essentially valuable code that you're afraid to change, code that carries your business but has become brittle or poorly understood over time.
Why does code turn into a legacy burden? Often, it's the natural byproduct of success and iteration. Your software grew fast to meet market needs, and not every early decision aged well. Perhaps parts of the system are running on outdated frameworks or unsupported tech. Maybe the original developers have left, taking vital knowledge with them. Documentation might be missing or obsolete. Over years of feature additions and quick fixes, the codebase might feel like a Jenga tower, one wrong move away from collapse.
It's important to drop the negative stigma around the word "legacy." Legacy code got you this far; it's the backbone of your current business."As soon as code is written and in production, it has become legacy" so legacy is a fact of life, not a mark of failure. Instead of blaming past developers or viewing legacy systems as worthless, embrace the legacy for what it is: a starting point full of hard-earned lessons and customer-driven refinements. This change in mindset is key.
The temptation to rewrite from scratch
(and why most rewrites fail)
When faced with snarled code and slow progress, many teams instinctively propose a do-over: "Let's rebuild the whole thing in [your favorite new framework]!" The idea of a clean slate is alluring. Who wouldn't want to ditch the crusty old system and create a pristine version 2.0 that fixes all past mistakes? In theory, a rewrite promises freedom: the chance to redesign with modern patterns, eliminate ugly code, and move faster without legacy baggage.
Consider these things first
Don't let the idea of a fresh start blind you to the very real risks. Before you toss your legacy code in the bin, be brutally honest about why it got messy and what a rewrite will truly entail.
- Hidden knowledge in old code
- Long time with no payoff
- Double the work (and cost)
- Morale and turnover risks
- "I promise we won't make the same mistakes", but you will make new ones
- The Big Bang deployment dilemma
- Scope creep and second-system syndrome
In most cases, you'll find that incremental fixes or deeper organizational changes (like better tests, training, or architecture improvements) address the root problems better than a total rewrite. In the next sections, we'll look at when a rewrite might be warranted, and more importantly, how to pursue a safer strategy that avoids lighting your product on fire.
How we help with legacy code
Our CTOs and staff engineers will join your team. Modernizing a legacy SaaS product is challenging, it demands technical savvy, strategic planning, and often a change in team habits. This is where madewithlove's approach shines. We're not another software agency that codes in isolation. We act as partners, embedding with your team to uplift your software and your engineers. Two key differentiators set us apart in legacy transformations:
Interim CTOs that are fearlessy honest, and senior staff engineers embedded within your team.
When does a software rewrite make sense?
There are rare instances where rewriting software from scratch may be justified. It's crucial to recognize that these are exceptional cases, and even then, rewrites should be approached with careful planning and safeguards. Below are a few situations where a rewrite might be considered the right course of action:
Starting from Scratch: If your product is essentially brand new, with no existing codebase or user base to consider, then a complete rewrite is more of a fresh start. This is typically the scenario when there's no legacy code to worry about.
A Complete Pivot or Audience Change: If your business has shifted to a different model or target audience, the existing software may no longer meet the new requirements. In these cases, the code could be hindering progress, and starting anew might be necessary. However, it's still worth evaluating if parts of the existing system can be salvaged before jumping into a full rewrite.
Code Beyond Repair: On occasion, a codebase becomes so tangled that even minor changes result in significant issues. If the code is tightly coupled, lacks testing, and every change involves a long debugging process, it may be time to consider a rewrite. This situation is rare and often results from long-term neglect.
Outdated Technology or End-of-Life Platforms: If your system relies on outdated technology or platforms that no longer have support, security vulnerabilities can become a real risk. In such cases, a rewrite may be necessary to ensure long-term viability, but it's crucial to choose a modern tech stack that will be sustainable. Sometimes, upgrading components one by one may be a more viable option than a full rewrite.
Major Paradigm Shift: If your product needs to support new capabilities, such as scalability or AI features, that your existing architecture cannot accommodate, it may require a new codebase. However, before committing to a rewrite, consider whether the new features can be added incrementally to the existing system without the need for a complete overhaul.
Drastic Changes in Business Logic: If the business logic driving your software has changed significantly, a rewrite might make sense. This could happen if many of your product's features are becoming obsolete, and your new roadmap requires building a product with a drastically different focus. In this case, rewriting to simplify and cut away unnecessary features can sometimes bring greater efficiency and focus to your product.
Even in these cases, proceed with caution. A rewrite should always be a last resort after exploring whether modular replacements or incremental improvements could resolve the issues. For example, if the problem is slow deployment, you might find that investing in automated CI/CD pipelines can address the bottleneck. If the lack of maintainability is due to missing tests, refactoring with proper test coverage could be an effective first step. Often, preparing for a rewrite (by documenting current behavior, adding tests, and clarifying requirements) can resolve many pain points, making a full rewrite unnecessary.
Meet are our CTOs in residence
Dimitri
Partner
from Belgium 🇧🇪
Jonas
CTO in residence
from Belgium 🇧🇪
Mike
CTO in residence
from Belgium 🇧🇪
Peter
CTO in residence
from Belgium 🇧🇪
Christophe
CTO in residence
from Belgium 🇧🇪
Brenden
CTO in residence
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See our other software experts
How we help you tackle legacy code
We've said it before, we are not just an agency. Two key differentiators set us apart in legacy transformations:
CTO in Residence (Fractional CTO service)
Sometimes, what a struggling legacy project needs most is strong technical leadership. Our CTO in residence service provides exactly that: an experienced Chief Technology Officer on a flexible, part-time basis with your company.
Our CTOs become hands-on team members, available a few days a week to guide your technical strategy and architecture decisions. They're supported by a whole bench of senior engineers and product experts at madewithlove.
Read more about our CTO as a ServiceStaff engineers in the trenches
Having a great strategy is half the battle, you also need skilled hands to implement it. That's where our Senior Staff Engineers come in. We embed seasoned engineers directly into your development team for the duration of the engagement.
Our engineers pair program with your devs, review code together, and introduce best practices. We believe in teaching you to fish, not just giving you a fish. When our engineers work alongside yours, improvements happen on two levels: the codebase gets better and your team gains skills for the future.
We keep your users in mind throughout. Our team implements changes to minimize downtime and avoid regressions. Your customers shouldn't even realize a "legacy rescue" is happening, except that suddenly the app feels snappier and more reliable.
More about our software engineering servicesWhat you'll achieve with our help
By the end of an engagement with us, you'll have:
- A cleaner, more maintainable codebase (likely with a significant reduction in bugs and an increase in automated test coverage).
- Faster deployment cycles and a team that's confident in deploying frequently.
- Improved team morale: developers feel empowered by new skills and the ability to ship improvements continuously.
- Processes and tools in place to sustain high code quality (linters, CI pipelines, code review standards, etc.).
- A clear technical strategy for the future, often documented by our CTO in residence so you have a compass going forward.
Above all, you'll know that you didn't just apply a band-aid, you truly transformed your legacy "brownfield" project into a modern, thriving software product. We have countless success stories, from helping a startup migrate off a brittle monolith to guiding a scale-up in refactoring their core service with zero downtime. While we can't name names here, we'd be happy to discuss relevant case studies in a call.
Evolving instead of replacing: the power of incremental modernization
In our experience working with dozens of SaaS teams, gradual refactoring and improvement (“evolution, not revolution”) is the hero that never gets enough credit. Incremental modernization means continuously improving your existing codebase in small, safe steps,all while it remains in production serving your customers. This approach embraces the Boy Scout rule: “Leave the code better than you found it.” Over time, those small changes add up to a radically improved system, without the trauma of a do-over.
Why choose incremental modernization over a big rewrite?
Much lower risk: By changing one component or one small aspect at a time, you greatly reduce the chance of catastrophic failures. If something does break, it's a contained issue, not a 2-year project going "bang" on launch day. Think of it like swapping out a car's engine while still driving versus building a new car and hoping it runs on the first turn of the key. With careful refactoring, you're never far from a working state, so you can course-correct quickly.
Continuous delivery of value: Incremental improvements allow you to keep shipping updates and features regularly, even as you modernize. Users see the product getting better steadily (new features, performance boosts, UI updates) instead of radio silence for a year followed by a massive change. This keeps you competitive and your customers happy. In fact, mature engineering teams aim to deploy code to production multiple times a day as a habit. Adopting that mindset forces you to make bite-sized, reversible changes rather than giant leaps.
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Client testimonials
Here's what people think about us
Lawfty
A nationwide network of vetted injury lawyers
CTO Coaching from madewithlove has been a game changer for me. Clive has helped me navigate the challenges we faced as we kicked off the rebuild of our application and doubled our team size. We also work on identifying my leadership style and ensuring team values are clearly dictated to my team. I wish I started sooner!
Elizabeth Rotunno (Director of Engineering)
Phished
Revolutionize the cyber awareness of your company
Madewithlove has been a fantastic partner for over two years. They helped us scale our team and build a future-proof platform that grows with our business. Their expertise in scalable architecture, pragmatic approach and overall professionalism has been key to our success. Highly recommended!
Arnout Van de Meulebroucke (CTO)
Helpper
A sharing economy platform for budget holders who need or are seeking additional support
In a short time, madewitloves interim CTO has noticeably improved how our development team works. The extensive experience and expertise have made our team more efficient and effective. In this way, our team managed to establish a solid foundation for future growth. The straightforward and expert advice on technical decisions, especially with complex issues, has been very valuable for our team. During a period of growth, this guidance has greatly helped us, allowing us to look to the future with more confidence.
Dries De Roeck (Product manager)
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We'll help you figure out the best way to level up your Saas product: whether it's through our fractional CTO services, software engineering, or a mix of both.
We are getting booked up pretty quickly, so the sooner you get in touch, the sooner we can help you.