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Alexandr Sopilnik

I Build Apps and Fix Broken & AI‑Built Ones | TypeScript, React, Rust

If your backend is slow, broken, or was generated by AI and nobody can maintain it, I can fix it.

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Work

Election trading desk — Supabase backend

A Supabase backend for a desk that trades election prediction markets. 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. It also has a news feed, RAG prep on pgvector and CI on every push to main.

Supabase · PostgreSQL · TypeScript · Deno · pgvector · Qwen

Formline Admin — admin panel

The panel is where orders are processed, the catalog is kept and stock is tracked. Staff have different access rights, and sign-in can be protected with two-factor authentication. Each visitor gets a private sandbox with no sign-up, kept apart by PostgreSQL row-level security.

Next.js · TypeScript · PostgreSQL · Drizzle · Docker

Formline — poster store

A storefront with collection filters, a cart and a Stripe checkout in test mode.

Next.js · TypeScript · Tailwind · Stripe

Bookkeeper Tweaks — Chrome extension

Four small fixes to the Xero pages bookkeepers use every day: an Approve button that does the action you choose, invoice printing without a PDF download, a pager at the top of long lists and sorting by description in Find and recode results. It runs in the browser and sends nothing to the developer or to third parties. Not affiliated with Xero.

TypeScript · Manifest V3 · Vitest · Playwright

reqwest-rotate — Rust crate

Proxy and rate-limit rotation for reqwest.

Services

Build

Websites and web apps from $80

A website that works on phones, tablets and desktops, loads fast and belongs to you afterward. I design the interface and code it by hand in React or Next.js. When the site needs a backend, I write that too, on Node.js or in Rust. Everything ships to your repository and your hosting, in your accounts. No builder lock-in and no monthly fee to me.

At the starting price
One responsive page: a landing page or a one-page company site, with your content, deployed and live.
Larger
Additional pages, forms, an admin panel, a database and more.
Front end from a Figma design from $60

You have a design and a backend, and you need the part users actually see. I turn Figma screens into a React or Next.js front end in TypeScript, responsive from phone to desktop, and connect it to your API. Every screen has loading, empty and error states. Spacing, type scale and colors come from the Figma file.

At the starting price
One screen from your Figma file, responsive, typed and connected to your API.
Larger
More screens with forms and validation, sign-in through your auth provider, shared components and tests for the main flows.
Mobile apps for Android and iOS from $100

A mobile app that shares code with your web product, or a first app to test an idea. I build it in React Native with TypeScript, so one codebase covers Android and iOS. I connect it to your backend and hand over builds ready for testing and store submission. The app is published from your developer accounts under your name, and the code stays in your repository.

At the starting price
Up to three screens with navigation and data from your API, as an Android build you can install.
Larger
More screens, sign-in through your backend, iOS builds through TestFlight, push notifications, offline use for the main screens, and builds ready for Google Play and the App Store.
Desktop applications for Windows, macOS and Linux from $120

A desktop application is the right answer when the work happens on the machine and not in a browser: files that never leave the office, a tool the team opens every morning, a window that keeps working when the connection drops. I build such applications in Rust, with the interface in Tauri.

At the starting price
One application with up to three screens for the platform you name, a running build early in the project and the source in your repository.
Larger
Builds for all three systems, a local database with search, CSV or Excel import and export, automatic updates and installers.
Chrome extensions from $40

A useful extension does one small job, such as saving what you are looking at or pulling numbers off a page. I build new ones in JavaScript or TypeScript on Manifest V3. I also fix existing ones broken by a Chrome update or a site redesign, or stuck on Manifest V2, which the Chrome Web Store no longer accepts. Every permission comes with a written reason, and the extension is published from your own developer account.

At the starting price
A fix for one reproducible problem in your extension, with a note on what caused it.
Larger
A new extension with up to five screens and saved settings, an existing one moved to Manifest V3, versions for Firefox and Edge, and a Chrome Web Store listing ready to submit.

Fix and improve

Bug fixes in JavaScript, React, Node.js and Next.js from $25

Something in your project broke or got slower. I reproduce the bug, find the cause and fix it. Then I write down what went wrong, what changed and how I checked it. The fix arrives as a pull request, a patch or a change on the live site, whichever suits you. I also work on projects someone else started.

At the starting price
One reproducible bug found, fixed and explained.
Larger
More bugs fixed, with a written summary and a list of other problems I noticed.
Fixing AI-generated apps before launch from $40

Your app works when you click through it, but you are not sure it will hold up with real users and real money. In an app built with Lovable, Bolt, Cursor or v0, I find what breaks, leaks or blocks the launch, then fix it in your code without starting over. I start with what generated code usually gets wrong: database access rules, secret keys that ended up in the browser, payment webhooks and error handling.

At the starting price
A written report before launch: every problem, where it is, why it matters and what the fix takes, worst first.
Larger
Fixes from the report in your repository, one commit per fix, tests for sign-in and payments, and a deployment you can repeat without the builder.
Speeding up React and Next.js apps from $75

Your app got slower one release at a time. I measure which problems actually cost your users time, then fix them. You get LCP, CLS, INP and bundle size per route, measured before and after on the same throttled connection, in one table. Work happens on a branch in your repository, commit by commit.

At the starting price
An audit of one page, then the fixes that move those numbers.
Larger
More routes, tuned rendering and caching, and a bundle budget in CI so the next release cannot quietly undo the work.
Moving a legacy front end to React or Next.js from $60

Your front end still runs on jQuery, old class components or an outdated Next.js setup, and every change takes longer than it should. I move it to modern React or Next.js in TypeScript one page at a time while the product keeps running: old and new code work side by side, URLs and the backend stay as they are, and each page switches over only when you decide.

At the starting price
A written migration plan for your front end and one small page moved as a working example.
Larger
More pages moved, shared components, TypeScript types for the data, and tests for the main flows.
WordPress and WooCommerce sites from $25

New WordPress sites and WooCommerce stores, and work on the ones you already have. I build custom themes from your design or a site you like, set up WooCommerce with the checkout your customers need, and keep the admin simple enough for your team to add pages and products without calling a developer. On existing sites I fix what broke after an update, speed up slow pages and checkouts, and rebuild pages that became hard to edit.

At the starting price
One reproducible problem on your WordPress site found, fixed and explained.
Larger
A new site or store built from your design, with WooCommerce, forms and the pages you need, deployed to your hosting.

Backend and infrastructure

Backend services and APIs in Rust from $50

A REST API on axum, a worker that processes files or a queue, or a service that sits between your system and someone else's API. Every service comes with tests, a README and the source in your repository.

At the starting price
One service with up to three REST endpoints, or one worker reading files or a queue you already run.
Larger
More endpoints with PostgreSQL, token auth with roles, a background worker, Docker, and a CI workflow that builds and tests on every push.
Backends on Node.js with Express or NestJS from $60

I write the REST API your web or mobile app talks to, in TypeScript on Node.js with Express or NestJS. I also build workers for uploaded files or queued jobs and connect your app to third-party APIs. Data goes to PostgreSQL, MongoDB or Redis, and every endpoint gets input validation and tests.

At the starting price
Up to three REST endpoints or one worker, with validation, tests and a README.
Larger
More endpoints backed by PostgreSQL or MongoDB, a Dockerfile, token auth with user roles, a queue worker and CI.
Row-level security in PostgreSQL from $40

If your app code alone decides who can read which rows, one missed check lets a user see someone else's data. I move the access check into PostgreSQL itself with row-level security policies and roles, then prove with tests that it holds. The same policies work in Supabase, which runs on PostgreSQL.

At the starting price
A review of the existing or missing policies for up to five tables, with a query that shows each gap.
Larger
Policies and roles for more tables as migration files, tests that sign in as different users, subscription plan limits enforced in the database, and the tests running in CI.
Docker and CI/CD for your app from $30

If your app runs on one laptop and ships by hand, I put it in Docker, add a GitHub Actions or GitLab CI pipeline that lints, tests and builds it on every push, and set up deployment from the repository to your server or platform. Keys and tokens live in your CI secrets, not in the code, and the README says how to run, release and roll back.

At the starting price
A production Dockerfile, a Compose file for local runs and a README.
Larger
A pipeline on every push and pull request, then automatic deployment to your Linux server, Railway, Fly.io or Vercel on every merge.
Command-line tools in Rust from $40

Rust tools for the jobs someone does by hand every week: converting or checking files, renaming and sorting in bulk, or calling an API and saving the result as CSV or JSON. A tool can run on a schedule and report what it did. It ships as one binary, with nothing to install on the machine that runs it, and stays fast on large files.

At the starting price
One tool with up to three commands, CSV and JSON in and out, tests, a README and a binary for your platform.
Larger
More commands, a validated config file, binaries for Windows, macOS and Linux, parallel processing with a progress bar, and a release workflow.

How I work

Contact

Reply the same day, Monday to Friday, 10:00–20:00 Almaty time (UTC+5).