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Tsimafei Yefimenka
RUENPL

Experience

Where I worked, in what role, and what outlived me. The chat knows all of it too.

  1. 05.2026 — present

    Freelance AI Trainer & Prompt Engineer

    Alignerr, Outlier

    Remote

    • —Training and annotating models on real code: evaluating and ranking LLM output on code-generation tasks.
    • —Validating model-written code. Where it holds up, where it breaks, and why a developer's review is still the check that matters.
    • —Designed prompt engineering workflows for technical evaluation tasks, improving annotation consistency across a distributed reviewer team.
    LLM evaluationPrompt engineeringJavaScriptTypeScriptReact

  2. 03.2025 — present

    JavaScript & React tutor, freelance development

    Preply, freelance

    Remote

    • —350+ hours of one-on-one JavaScript and React tutoring, taking students from fundamentals to job-ready portfolio projects.
    • —At least four students have since been hired in IT, in Israel, Poland, Cyprus and Canada.
    • —A freelance project on global reforestation: pulling tree-planting data from several sources into one openly published picture.
    JavaScriptTypeScriptReactNode.jsMentoring

  3. 04.2024 — present

    Senior Software Engineer

    Godel Technologies Europe

    Łódź, Poland — hybrid

    • —Led the migration of a core client-facing module to React + TypeScript: 30% smaller bundle, Lighthouse performance up from 62 to 91.
    • —Cut critical production bugs by 40% through Jest/React Testing Library coverage and a stricter review process across a team of five.
    • —End-to-end browser tests on Playwright and Puppeteer, including tooling of his own: when a test fails in the pipeline, screenshots are captured during the run itself, so a failure does not have to be reproduced by hand to see what broke.
    • —Mentored two mid-level engineers, shortening their onboarding by two weeks.
    • —07.2023 — 12.2024, an internal engineering-maturity programme: reviewed around 30 company projects end to end with their teams and UK clients against an in-house assessment framework, to see where the process breaks and what to fix first. Project satisfaction scores rose by 20%, and teams closed about 70% of the recommendations within a quarter.
    • —Delivered two BFF/backend applications end to end with spec-driven development in a team of three, scaffolding from specs with Claude Code, Windsurf and Codex, 30–40% faster delivery.
    ReactNext.jsTypeScriptNode.jsExpressMonorepoJestPlaywrightPuppeteer

  4. 09.2021 — 04.2024

    Software Engineer

    Godel Technologies Europe

    Minsk, Belarus → Łódź, Poland

    • —09.2021 — 09.2022, a ship tracking platform: an interface built around a 3D model of the vessel with decks, cameras and nodes, a fleet map, and telemetry intake over UDP into TimescaleDB, a continuous feed from 50+ vessels at once.
    • —From 09.2022, one of the UK's largest price comparison websites, impartial comparison of financial products and services.
    • —Raised unit and integration test coverage to 100%.
    • —Migrated all services to GitLab together with DevOps.
    • —Shipped a UI redesign across several products.
    • —Took part in a major refactoring effort onto a new framework: 25% better page performance with no loss of functionality.
    • —Contributed to company-wide work on code and process compliance across projects.
    ReactReduxTanStack QueryTypeScriptGraphQLApollo ClientNode.jsTimescaleDBMonorepoDockerJestPlaywright

  5. 02.2018 — 08.2021

    Full Stack Engineer (Vue, Laravel)

    AKDev Group

    Minsk, Belarus

    • —Started as an intern on an invoice-building platform, then worked part-time alongside university and moved to full time in 2021.
    • —RadioHeart (08.2018 — 02.2019): an internet radio platform with 24/7 uptime. Built the DJ console on the Web Audio API. Two decks with crossfading, jingles and ads, a microphone with per-channel volume and a headphone return of the live mix.
    • —CleverStart (03.2019 — 08.2019): mental arithmetic for children. Extended the abacus task generator, rebuilt the landing page for conversion (+20% trial-lesson sign-ups) and helped build the olympiad module.
    • —Online school (08.2019 — 08.2021): designed and implemented the school module architecture and integrated a WYSIWYG editor with a custom menu and image/video components.
    • —Added YouTube and Vimeo embedding with navigation by timecodes from the original platforms.
    • —Upgraded the project from Webpack 2 to Webpack 4.
    VueVuexReactReduxLaravelPHPNode.jsWeb Audio APIMySQLPostgreSQLDockerSASSElasticSearchGrafana

About the dates

  • —12.2020 — 05.2021: six months of mandatory military service; the AKDev Group work paused for that period.
  • —Summer 2022: relocation from Minsk to Łódź within the same company. The first year at Godel was worked from Minsk.
  • —April 2024: promoted to Senior Software Engineer within Godel.

Education

  • Belarusian State University, Minsk — B.Sc. in Mathematics and Mathematical Cybernetics, 2016–2020. Studied algorithm design, data modelling, statistical analysis and computational systems.