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Alexandr Sopilnik

Full-Stack Developer | Rust, TypeScript, JavaScript | AI Integrations

📍 Located in: Kazakhstan 🕐
🎯🤝 Open to one-off or long-term work ⏱️ 40 hrs/week available
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⭐ Zinner Level 1
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🛡️ Verified since September 2026

Member since
Sep 2026
Zinns listed
18
Avg response
0h
Last active
2 hours ago

About

Full-stack developer with 10+ years in IT. I build and fix web, desktop and mobile apps, APIs and Chrome extensions in TypeScript, JavaScript and Rust. That includes Lovable and Bolt apps that aren't ready for real users yet. I also add AI features to existing products: LLM integrations, document search and chatbots.

Stack:
- Languages: TypeScript, JavaScript, Rust, SQL, HTML, CSS/SCSS
- Front end: React, Next.js, responsive interfaces that I design myself and build without templates
- Back end: Node.js (Express, NestJS), Deno, Rust (axum), REST and gRPC APIs, Kafka
- Databases: PostgreSQL with row-level security, MySQL, MariaDB, MongoDB, Redis, Supabase
- AI: LLM integrations that check the model's output before saving it, vector search on pgvector, RAG chatbots that answer from your files
- Platforms: WordPress and WooCommerce, multilingual sites with WPML, Chrome extensions (Manifest V3), desktop apps with Tauri, mobile apps in React Native
- DevOps: Docker, Kubernetes, Helm, werf, CI/CD on GitHub Actions and GitLab CI
- Integrations and automation: payment providers, third-party APIs, scheduled jobs with an alert if one stops running

What I take on:
- Apps built with Lovable, Bolt, Cursor or v0 that work for the founder but aren't ready for real users: broken sign-in, failing payments, missing access rules, code nobody wants to touch
- New web apps from the database to the interface, plus landing pages and multilingual sites
- AI features in an existing product: LLM summaries and scoring, search over your documents, chatbots that cite their source
- Bug fixes and performance work on slow pages, API endpoints and database queries
- Backends, APIs and command-line tools in Node.js or Rust
- Desktop, mobile and browser-extension projects

Experience:
- Supabase in production: scheduled TypeScript functions, LLM steps whose output is checked before it is saved, pgvector search, an alert whenever a scheduled job stops running, and CI on every push to main
- Access control inside PostgreSQL: row-level security policies and a separate role for each subscription tier, so users see only what their plan allows
- A legacy PHP backend rewritten in Node.js/TypeScript without breaking its API; median response time on the main endpoints fell roughly 3×
- A jQuery front end moved to React page by page while the product stayed live
- Rust backends: axum microservices on PostgreSQL and Redis that talk to each other through Kafka and gRPC, with a REST API for the front end
- Open source: reqwest-rotate, my Rust crate for proxy rotation, per-host rate limits and retries in the reqwest HTTP client, published on the official Rust registry
- Live demos and client work are in my portfolio, and my public code is on the GitHub account linked to this profile.

How I work: async and in writing. I write the scope down before I start. Well-defined work gets a fixed price; open-ended work is billed hourly until the scope is clear. You get a short written update at the end of each working day, and no calls are needed. I work 10:00–20:00 Almaty time (UTC+5), which covers most of the European working day and the start of the US East Coast day.

To start, send me what you have (a repo, a live app or a short description) and what you need. I'll reply with a written plan and a price. If you'd like to see how I work first, we can begin with one small fixed-price task, such as a single bug fix.

Skills

Technologies and expertise this freelancer specialises in.

Categories

Service areas this freelancer is available for.

Portfolio

Formline Admin: Next.js admin panel

The back office for my Formline demo store, open to try with no sign-up: every visitor gets a private sandbox with demo data. Staff process orders, keep the catalog and track stock, and paid Stripe test orders from the store arrive through a signed webhook. Four staff roles, from owner to read-only viewer, have different rights; sign-in supports an authenticator app and passkeys. Built with Next.js, React and TypeScript on PostgreSQL with Drizzle; row-level security keeps every workspace apart. It runs in Docker, with Vitest and Playwright tests in CI.

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Election trading desk backend

Client project: I extended the Supabase backend of a desk that trades election prediction markets. My scheduled TypeScript functions snapshot Kalshi order books, find new election markets, draft candidate profiles and raise alerts; an LLM (Qwen) writes hourly race summaries for the traders and scores YouTube comments. I also added a news feed with search, RAG prep on pgvector and CI on every push to main. Every job I added reports a heartbeat, and an hourly watchdog alerts when a job goes quiet or prices stop arriving. The owner got a setup guide and a walkthrough video.

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Bookkeeper Tweaks: Chrome extension

A free, open-source Chrome extension (Manifest V3) with four small fixes to the Xero pages bookkeepers use every day. The Approve button on an invoice does the action you choose, approved invoices print without downloading a PDF first, long lists get page navigation at the top, and a button sorts the current Find and recode page by description. It runs only on go.xero.com, with one permission and no analytics or remote code. Built in TypeScript; CI runs lint, type checks, Vitest unit tests and Playwright end-to-end tests of the built extension. Not affiliated with or endorsed by Xero Limited.

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Formline: Next.js store with Stripe

A storefront you can click through: 16 posters in 4 collections, filters and search that stay in the URL, a cart, light and dark themes, and a checkout that ends in a demo order or a real Stripe Checkout session in test mode. I built it as a Next.js static export in TypeScript with Tailwind CSS. Poster images are generated from SVG templates and rendered to PNG at build time. Card payments go through a Cloudflare Worker that re-prices the cart on the server and verifies Stripe's webhook signature. Vitest and Playwright tests run in GitHub Actions on every push; pushes to main deploy the site.

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reqwest-rotate: open-source crate

A small reqwest wrapper for scrapers and API clients that need proxy rotation, per-host rate limiting and retry with backoff, without pulling in a middleware framework. Published on crates.io with docs, CI and about two hundred tests.

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Bilingual personal site in Next.js

A one-page personal site in English and Russian, with a services section and links to my demo projects. I designed and built it with Next.js, React and TypeScript as a static export, styled with plain CSS Modules and no UI framework. It has light and dark themes, and a social preview image for each language is generated at build time. GitHub Actions builds and deploys it to Bunny CDN, which adds security headers and redirects www and plain HTTP to the main HTTPS address.

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Rust microservices, EdTech backend

I built the backend: Rust services on axum, Kafka for events between services, PostgreSQL and Redis, gRPC inside, REST for the React front end. Docker, CI/CD. Client under NDA.

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PHP backend rewritten in Node.js/TS

Rewrote the backend of a client's web platform from legacy PHP to Node.js/TypeScript and kept the public API compatible, so the front end shipped unchanged. Median response time on the main endpoints dropped by roughly 3x. Deployment moved to Docker with CI/CD. Client under NDA.

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jQuery to React migration, live app

Moved a jQuery front end to React page by page while the product stayed in production. jQuery is gone, the UI is component-based, and new features are built on the React side. Client under NDA.

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React + Node.js + PostgreSQL app

Built the front end, backend and database for a client: React, TypeScript on Node.js, PostgreSQL, shipped as one deployable service with CI/CD. Client under NDA.

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Rust CLI tools and scrapers

Command-line utilities, scrapers and parsers in Rust that collect narrow-domain data for clients (async, reqwest, scraper, serde). Proxy rotation and rate-limit handling when a site requires it; targets range from static HTML to JS-rendered pages. Sources and datasets are under NDA.

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Gladiator-school sim in Rust/Bevy

Management sim with pre-simulated combat and an event log, a d20 hit-location system, utility AI and an economy layer. Built on Bevy ECS, with an automated test suite.

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Zinns — Ready to Purchase Services (18)

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I Will build a Node.js backend with Express or NestJS

$60.00
🔒 No Platform Fees for Buyers

Micro Zinns (1)

Small, fixed-price tasters from $5 — quick jobs you can buy in one click, or a low-risk way to try a Zinner before a bigger order.

Micro Zinn

I will fix a bug in your JavaScript, React or Node.js web app

$20.00
🔒 No Platform Fees for Buyers
Portfolio builder Service taster Quick small job
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