Should I Use Ready-Made Code or Build Everything Fresh?

When you're building a mobile app, you'll face this question dozens of times: should I use code that already exists or write it myself from scratch? It's one of those decisions that seems simple at first but gets complicated fast. I've watched clients spend weeks building features that could have been implemented in days with the right library, and I've also seen apps collapse under the weight of too many dependencies they didn't really need. Both scenarios are expensive mistakes.

Here's what most developers wont tell you—there's no single right answer. I know, not what you wanted to hear! But its true. Every app project sits somewhere on a spectrum between "use everything off the shelf" and "build it all ourselves", and where your project lands depends on factors most people dont consider until its too late. Your timeline matters. Your budget matters. Whether you're building an MVP or a long-term product matters. The technical expertise of your team matters.

The question isn't really about code at all—it's about understanding what makes your app unique and what's just plumbing that needs to work reliably.

Over the years I've built apps for healthcare companies that absolutely needed custom solutions for data handling (GDPR compliance isn't optional), and I've built e-commerce apps where using battle-tested payment libraries was the only sensible choice. The trick is knowing which parts of your app deserve custom attention and which parts should leverage proven solutions. That distinction will save you months of development time and probably a small fortune in debugging costs down the line. And honestly? Getting this wrong early on can derail your entire project before you've even launched.

What Are Third-Party Libraries and Why Do They Matter?

Right, so third-party libraries are basically chunks of code that other developers have written and made available for anyone to use. Think of them as pre-built tools that handle specific jobs—things like processing payments, displaying maps, sending notifications, or managing user authentication. Instead of writing all that code yourself from scratch, you can drop these libraries into your app and get those features working much faster.

I've used hundreds of these over the years, and honestly they can be a lifesaver. When we built a fintech app that needed to handle complex date calculations across different time zones, we used a library called Moment.js instead of spending weeks writing our own solution. It saved us probably three weeks of development time and thousands of pounds in costs. But here's the thing—every library you add becomes a dependency, and dependencies can cause problems down the line if they're not maintained properly or if they conflict with other code.

The tricky bit is knowing which libraries are worth using and which ones will cause you headaches later. Some are maintained by huge tech companies like Google or Facebook, whilst others are passion projects built by a single developer who might lose interest next year. I've seen apps break because a critical library stopped being updated and became incompatible with new versions of iOS or Android. Its not fun explaining to a client why their app suddenly crashes because someone halfway across the world stopped maintaining a piece of free code.

Common Types of Third-Party Libraries

• Authentication libraries (handling user login and security)
• Payment processing SDKs (Stripe, PayPal integrations)
• Analytics tools (tracking user behaviour and app performance)
• UI component libraries (pre-designed buttons, forms, and layouts)
• Networking libraries (managing API calls and data transfer)
• Image processing tools (resizing, filtering, and optimising photos)

The key question isn't whether to use third-party libraries—you almost certainly will—but rather which ones to trust with your apps success. Some libraries have become industry standards that practically every app uses; others are risky bets that might leave you scrambling for alternatives when they inevitably get abandoned.

The Real Cost of Building Everything From Scratch

I've had clients come to me saying they want to build "everything custom" because they're worried about dependencies or want complete control. I get it, I really do. But here's what they don't realise until we sit down and do the maths—building a simple authentication system from scratch can easily add 3-4 weeks to your timeline. That's not even including the security testing and edge cases you'll need to handle. When you're paying a development team, those weeks add up fast; we're talking £15,000-20,000 just for login functionality that a library like Firebase Auth or Auth0 could give you in a few days for a fraction of the cost.

The time factor is just the start though. I worked with a fintech startup that insisted on building their own payment processing system because they wanted "full control" over the transaction flow. Six months and £80,000 later, they'd created something that still didn't have all the fraud detection features that Stripe includes out of the box. And then they had to maintain it, which meant keeping a developer on retainer to handle updates and security patches. It was bloody expensive, and honestly? Their custom solution wasn't any better than what already existed.

Before deciding to build something custom, ask yourself: "Is this feature what makes our app unique?" If the answer is no, you're probably wasting money reinventing the wheel.

What Building From Scratch Actually Costs You

Let me break down the real costs because its not just about the initial development time:

• Development time (usually 3-5x longer than using existing libraries)
• Ongoing maintenance and security updates
• Testing across different devices and edge cases
• Documentation so other developers can understand your code
• Bug fixes when things inevitably break in production
• Opportunity cost of not working on features that actually differentiate your app

The opportunity cost is the one that hurts most. Every hour your team spends rebuilding image caching or network requests is an hour they're not spending on the features that make your app special. I've seen this play out dozens of times—teams get so focused on building their own infrastructure that they never get around to perfecting the user experience that would actually make people choose their app over competitors.

When Ready-Made Code Makes Perfect Sense

There are situations where using third-party libraries isn't just sensible—its the smartest business decision you can make. I've built enough apps to know that writing everything from scratch is often just expensive pride talking. When we built a fitness tracking app for a health startup with limited funding, we used established libraries for mapping, workout tracking algorithms and nutrition databases. The alternative? Spending six months building features that already existed and worked brilliantly. That money went into what actually made their app different instead.

Authentication and security are perfect examples. Unless you're a bank with dedicated security teams, you don't want to build your own authentication system; the risk of getting it wrong is too high and the consequences can be bloody expensive. We use Firebase Auth or Auth0 for most projects because they handle all the complex security stuff—password hashing, token management, social logins—far better than a custom solution ever would. I've seen startups waste three months building custom auth systems that still had security holes. Not worth it.

When to Reach for Ready-Made Solutions

Here's what I always use third-party code for, based on years of building apps that actually need to ship:

• Payment processing—Stripe and PayPal have spent millions on compliance and security
• Video streaming—building your own is insanely complex and expensive
• Analytics—Google Analytics and Mixpanel do this better than you will
• Push notifications—Firebase Cloud Messaging works reliably across millions of devices
• Maps and location services—Google Maps API is the standard for good reason
• Image processing—libraries like SDWebImage handle caching and memory management brilliantly

The pattern here? These are solved problems where your custom solution won't add real value to users. An e-commerce client once insisted on building custom payment handling. After reviewing PCI compliance requirements, they quickly changed their mind... the legal and security overhead alone would have doubled their development budget. Sometimes the boring answer is the right one.

When Custom Development Is Worth the Investment

I've worked on healthcare apps where we absolutely had to build our own encryption layer from scratch because the client needed to meet specific NHS security requirements that off-the-shelf libraries just couldn't handle. The cost? About three months of development time and a budget that made the client wince. But here's the thing—it was worth every penny because the alternative was regulatory non-compliance and potential patient data breaches. That's when custom development stops being a luxury and becomes a necessity.

There are a few clear situations where building from scratch makes sense, and I mean really makes sense, not just because someone wants to feel clever. First up is when you're building something that defines your competitive advantage. If your entire business model relies on a unique algorithm or a special way of processing data, you can't rely on the same libraries your competitors are using. I worked with a fintech startup whose whole selling point was their instant credit scoring system—we built that engine custom because it was literally the product itself.

When your core feature is what sets you apart from everyone else, using the same tools as your competitors is like trying to win a race with the same legs as everyone else

Performance is another big one. We built a custom video processing pipeline for an e-commerce client because existing libraries added too much latency to their product photography workflow. Sure, there were ready-made solutions, but they couldn't handle the specific combination of speed and quality the client needed. Custom code let us optimise for their exact use case, cutting processing time by 60%. Its not always about being different—sometimes its about being better at one specific thing that matters to your users.

How to Evaluate Code Libraries Before Using Them

I can't tell you how many times I've seen developers (myself included, early on) get burned by a library that looked perfect on paper but turned into a nightmare six months into production. The evaluation process is something I've refined over years of building apps across healthcare, fintech and e-commerce—and its honestly more about what the library doesnt tell you than what it does.

First thing I do? Check the last commit date and issue response times. If the maintainers haven't touched the code in eight months or there's hundreds of unresolved issues, that's a massive red flag. I learned this the hard way on a fintech project where we used a payment processing library that seemed solid but the maintainers had basically abandoned it; when iOS 14 dropped, we spent three weeks rewriting functionality that should've just worked.

My Four-Point Library Checklist

Here's what I look at before adding any dependency to a project, and I mean any dependency—even the small ones can bite you:

• Documentation quality and completeness (can you actually implement it without guessing?)
• Bundle size impact, especially for React Native where every kilobyte matters
• License compatibility with your project and any client restrictions
• Community size and whether major companies are using it in production
• Native module requirements because these can complicate your build process massively

The Numbers That Actually Matter

GitHub stars are nice but I care more about weekly downloads and the contributor count. A library with 50,000 weekly downloads and 20+ active contributors is far safer than one with 10,000 stars but only one maintainer. On a healthcare app we built, we specifically chose a charting library with lower stars but better maintenance because patient data visualisation couldn't break during an OS update—that decision saved us when Android 12 changed some rendering behaviour and the library was patched within days.

Also? Actually read through recent issues. You'll learn what breaks, what's poorly designed, and whether the maintainers are responsive or defensive. Its a bit tedious but spending an hour here can save you weeks later.

Managing Dependencies Without Creating a Mess

I've seen projects collapse under the weight of their own dependencies, and its not pretty. The worst case? A fintech app we inherited that had 47 third-party libraries, half of which hadn't been updated in over two years and three that were actively conflicting with each other. The app crashed on launch for 30% of users and nobody on the original team could figure out why.

Here's what I do now on every project—keep a dependency audit document that lists every single library, why we chose it, what it does, and when it was last updated. Sounds boring? Maybe. But it's saved us countless hours of debugging and prevented at least a dozen potential disasters. When you're three months into development and someone asks "why are we using this specific image caching library", you need to have that answer documented somewhere.

Set up automated dependency checking tools like Dependabot or Renovate that alert you when libraries need updating; waiting until something breaks is like ignoring that weird noise your car makes until it stops working entirely.

Version Lock Your Critical Dependencies

This is where a lot of teams get it wrong. They let their package manager automatically update to the latest versions, thinking they're staying current. But I've watched a "minor" update to a payment processing library break an entire checkout flow two days before launch. Now? We lock versions on anything critical—payment processing, authentication, data encryption—and only update them during dedicated maintenance sprints when we have time to test properly.

The 80/20 Rule for Dependencies

Most apps use about 80% of their dependencies for only 20% of their functionality. I regularly review our dependency list and ask "could we build this ourselves in a day or two?" If the answer is yes and the library is causing headaches, out it goes. We once replaced a 15MB date formatting library with 50 lines of custom code, shaved 2 seconds off our app launch time, and never looked back. For more complex scenarios, optimising how your app handles media can often be more effective than adding another dependency.

The Hidden Risks Nobody Talks About

I've seen apps completely break because of things that seemed harmless at first. Sure, everyone talks about security vulnerabilities and licensing issues, but there are other risks that catch people off guard—and these can be just as damaging to your project. When I was working on a healthcare app a few years back, we had a third-party analytics library that worked perfectly fine until Apple updated iOS. The library hadn't been maintained in eighteen months and suddenly our crash rate jumped from 0.2% to 8% overnight. It took us three weeks to fix because we had to rewrite that entire component ourselves.

One risk that really doesn't get enough attention is something called "dependency hell." Basically, this happens when Library A needs version 2.0 of Library C, but Library B needs version 3.0 of Library C, and they simply wont play nicely together. I've spent entire days trying to resolve conflicts like this, and sometimes there's no clean solution—you end up having to replace one of your libraries entirely. Its frustrating because you don't see it coming until you try to add something new or update your codebase.

The Real Dangers Worth Watching

Another thing that trips people up is the "bus factor"—what happens if the person maintaining your critical library disappears? I mean, open source is brilliant for many reasons, but it relies on people volunteering their time. I've seen popular libraries just stop getting updates because the maintainer got a demanding job or lost interest. For a fintech app we built, we deliberately avoided a really nice payment UI library because it was maintained by just one person with no backup contributors. That decision saved us months of work later when that library was abandoned.

• Abandoned libraries that stop receiving security patches or OS compatibility updates
• Bloated app sizes from including large libraries for small features (one client's app was 180MB before we optimised it down to 45MB)
• Privacy compliance issues where libraries collect data you didn't know about
• Performance degradation when libraries conflict or use resources inefficiently
• Vendor lock-in where switching costs become prohibitively expensive

The privacy thing has become huge recently. Some analytics and advertising libraries collect way more data than you'd expect, and with GDPR and similar regulations, you're responsible for everything your app does—even if it's third-party code doing it. I always audit what data each library accesses now because I've had clients face complaints about permissions their app was requesting that they didn't even know about. The library was asking for contacts access in the background and they had no idea until users started leaving angry reviews. When it comes to location data specifically, understanding privacy regulations becomes absolutely critical before you integrate any mapping or geolocation libraries.

Conclusion

After building apps for healthcare providers who needed HIPAA-compliant messaging systems and fintech startups racing to launch before their funding ran out, I can tell you there's no universal answer to the build versus buy question. It's always context. Always. What I've learned is that the best apps use a strategic mix—third-party libraries for the boring stuff that doesn't differentiate you (user authentication, payment processing, analytics) and custom development for the features that make your app special. When we built a food delivery app that needed to compete with the big players, we used Stripe for payments and Twilio for SMS notifications because rebuilding those would've been bloody mad, but we built the restaurant matching algorithm from scratch because that was the whole point of the app.

The developers I work with who make the smartest decisions are the ones who think in terms of value, not perfection. They ask "will building this ourselves make us more competitive?" rather than "can we build this ourselves?" Sure, you might be able to recreate Firebase's functionality, but why would you spend three months doing that when you could be testing your core product with real users? The apps that fail—and I've seen plenty—often fail because teams spent their entire budget building infrastructure that already existed instead of solving the actual problem their users had. Its not about choosing one approach over the other; it's about knowing which parts of your app deserve custom work and which parts should use proven solutions so you can ship faster and learn what your users actually want.