Portfolio BrandsApplication / Alex Kostyniuk

I build frontend with the same care COS puts into a garment: considered structure, nothing decorative left in, and finishing you notice only because everything feels right.

Senior Frontend Engineer · Full-stack Range · Stockholm

Alex Kostyniuk

Look 01 / Candidate

Alex Kostyniuk

COS
Materials
Next.jsReactTypeScriptTailwind CSSNode.jsGraphQLHeadless CMSGitHub ActionsAWSPostgreSQL

Why we're a considered match

Why COS should hire me

01

The exact stack
Next.js, React, and TypeScript with Tailwind are what I work in every day: App Router, server components, and the rendering trade-offs that decide how a storefront actually feels.

02

Frontend architecture
I design component-driven systems and state boundaries that hold up as teams and surfaces multiply, instead of ones that quietly rot into special cases.

03

Performance as a habit
I turned a ten-minute core workflow into a twenty-second one by challenging the architecture, not merely tuning it. Commerce pages reward exactly that instinct.

04

Full-stack range
I work fluently across TypeScript, Node.js, PostgreSQL, and AWS, and integrate REST and GraphQL services, so I can follow a feature past the UI when the feature needs it.

05

Technical leadership
I lead engineers, review code, set direction, and still ship. Code reviews and engineering standards are how I raise the bar without becoming a bottleneck.

06

AI-first development
I introduced agentic workflows at my current company and use them daily with judgment, testing, and review kept firmly in the loop.

Why I want to join COS

01

A brand where craft is visible
COS is built on exceptional quality and lasting design. That is the rare brief where frontend polish is not a nice-to-have, it is the product promise, rendered in a browser.

02

Composable commerce at scale
A headless e-commerce platform serving brand-unique experiences is genuinely hard, interesting work: content modelling, integration seams, and performance under real traffic.

03

In Stockholm, in the room
I am in Stockholm and I want to be on-site with product, design, and backend. The best decisions I have been part of happened standing next to the people making them.

How I work.

I start with either a problem to solve or a business idea. I shape it around customer needs and technical realities, and look for a solution that can serve many customers instead of just one. Once the core is clear, I work with Design team on the experience, break it down into a focused story, and leave it ready for a developer or me to build.

How I develop features

  1. 01

    Start with an agent

    I always work with an agent. For bigger features or bugs that aren't obvious at first, I use specific skills to help it focus. For smaller tasks, I explain what needs doing and jump in.

  2. 02

    Scope the solution

    When the work needs a plan, I turn it into a detailed spec, including edge cases and what done looks like.

  3. 03

    Implement with agents

    Once the task is clear, I let one or more agents build the feature.

  4. 04

    Create feedback loops

    Browser Use, types, and tests help the agents see what they built and catch their own mistakes.

  5. 05

    Check manually

    I still open the feature and use it myself, from start to finish.

  6. 06

    Run an agent review

    I ask fresh agents to review the work and catch anything the first ones missed.

  7. 07

    Review the code

    Then I read the diff myself and fix whatever is left.

  8. 08

    Babysit the PR

    Finally, an agent watches CI and review comments until the PR is ready to merge.

Outcome

The result is a feature that has been planned, built, checked, and reviewed from a few different angles, usually in much less time.

Portfolio BrandsCOS

Let's make COS feel online exactly as considered as it does in store.

COS × Alex

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