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Xenofon Gkioka / Full-stack developer

Toronto, Canada

Useful software.
Thoughtfully built.

I build full-stack applications, developer tools, and websites for real businesses. From the interface to the logic underneath.

Explore selected work View CV ↗
Need a website for your business? →
AZ Clean website: a Greek cleaning business with service information and direct contact actions
In the field / AZ CleanClient websites ↗

Developer intern / 2026

Mercell

Shipped a micro-frontend to production on a platform with 800,000+ users.

Developer / 2021

Spinworks

Worked on a B2B e-commerce platform.

Tools / Source available

Testing the tests.

Mutation testing for changed lines of code.

Reported benchmark ↗

01 / Selected work

From problem
to working code.

All engineering work ↗
01 / Engineeringprototype

ai-eng

Mutation testing scoped to the lines a change touches, to show whether existing tests would notice if those lines were wrong.

Role
Specification, benchmark design and review. The implementation was written by Claude Code from that specification, as the repository's README states.
Stack
JavaScript / Node.js / Babel / Vitest
Read case study →Source ↗Benchmark write-up ↗

60 real zod bug fixes were reverted one at a time; 1 was excluded because its own regression test did not reproduce the bug, leaving 59 scored. Surviving mutants flagged the reverted lines as weakly tested in 27 of those 59; zod's existing test suite caught none of them. (repository reported). Benchmark ↗

Terminal output from ai-eng on a one-line change to a discount function: four mutants on line 2, three survived and one was killed, giving a trust score of 25% with the verdict 'read every line'. It lists each surviving mutation, such as '&&' changed to '||', and one behaviour change on 1 of 33 generated calls. The command exits with status 1.
02 / Engineeringprototype

KykloC

A field-service app for small trade businesses: customers, appointments, jobs, payments and repeat work in one place, in Greek and English.

Role
Product direction and development. The project was scaffolded with Lovable and developed from there.
Stack
React / TanStack Start / Supabase / PostgreSQL / Vitest
Read case study →Try it on this device ↗

Anyone can try it without an account: the trial runs in the browser with sample data that stays on the device. (executed). Live trial ↗

KykloC's schedule for Wednesday 28 October in the on-device trial: three jobs totalling 383.78 euros, each with a time, customer, services, address, assigned worker, and status labels such as Scheduled, Completed, Paid and Unpaid. The names and addresses are the app's built-in sample data.
03 / Client websitelive

AZ Clean

A Greek-language website for a cleaning business in the southern suburbs of Athens, built around calling or sending a photo for a quote.

Role
Redesign and front-end development.
Stack
React / Vite / GitHub Pages
Read case study →azclean.gr ↗

The site is live on the business's own domain. (executed). Live site ↗

The AZ Clean home page on desktop: a dark hero photo of a worker in a branded T-shirt cleaning a mattress, a Greek headline meaning 'The right way to clean', service areas, a 'Call us' button and a 'Send a photo' button.

An illustrative boundary mutation

Would a test notice one changed character?

ai-eng changes code to probe the tests around it. This small example shows why the input matters; it does not run the project’s test suite.

Originalreturn amount > 0true
Mutantreturn amount >= 0true

Both versions return the same result. This input alone would miss the changed boundary.

02 / Run the code

C++.
In your browser.

ArenaCore is a turn-based combat engine. Choose an opponent, change a fighter’s attributes, and let the compiled engine calculate each round.

Read the source ↗
ArenaCore / Interactive C++

Choose.
Fight.
Reset.

C++ → WebAssembly → browser
Xenofon Gkioka

03 / The person behind the work

A practical route
into software.

IT support in Athens. B2B development at Spinworks. A move to Toronto, work in construction, and software studies at Seneca. Then an internship at Mercell in Copenhagen.

I like work with a clear purpose: understand the problem, build something useful, and check that it works.

More about me →