Can you modernize an app without source code?

If you own the app or have the right to change it, I can work out its behavior by studying it while it runs. With source code the process is faster and safer. I listen to the situation and tell you whether it is feasible.

Is it better to rewrite from scratch or migrate piece by piece?

Moving piece by piece is usually less risky because the working system is never cut off. Rewriting can make more sense when the app is very small or its foundation is unusable.

Will my site keep working during the migration?

My aim is to avoid downtime. Running the old and new versions side by side and switching when the new one is ready is how that works.

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Modernizing a legacy application

Short answer

I study an old or undocumented application, work out how it behaves and move it to a modern stack while keeping that behavior. Moving a frontend from Create React App to Vite made builds 3 times faster, and moving from AWS managed services to a VPS cut costs. I work on applications you own or have the right to change.

Message on WhatsApp+90 539 980 47 25 Contact

How I work

I study the application while it runs to find out what it does and which data it touches.
We document current behavior and identify the critical flows.
I move it piece by piece, starting with the lowest-risk part; the old and new versions can run side by side for a while.
I test each step against the old behavior.

The goal is not to rewrite from scratch but to reach a modern structure without losing work that already functions.

When it makes sense

You need to add features to an app with missing source code or documentation
Builds are very slow or the libraries are outdated
Server costs are higher than they should be
The site's search visibility is low for technical reasons

My migration experience

SubmitApp: moved the frontend from Create React App to Vite, making builds 3 times faster. Restructured the architecture; the Lighthouse SEO score went from 50% to 98%.
Qrispy: moved AWS managed services to a VPS and reduced costs.
Qrispy: rewrote the existing mobile experience with Expo and React Native.

Questions

Can you modernize an app without source code?: If you own the app or have the right to change it, I can work out its behavior by studying it while it runs. With source code the process is faster and safer. I listen to the situation and tell you whether it is feasible.
Is it better to rewrite from scratch or migrate piece by piece?: Moving piece by piece is usually less risky because the working system is never cut off. Rewriting can make more sense when the app is very small or its foundation is unusable.
Will my site keep working during the migration?: My aim is to avoid downtime. Running the old and new versions side by side and switching when the new one is ready is how that works.

Tell me about your project

A short note is enough. We pin down the scope and discuss price and timeline together.

WhatsApp +90 539 980 47 25 myyilmaz97@gmail.com Fill in the form

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Written by Mert Yılmaz, freelance fullstack developer.