Arsen Shkrumelyak
Software Engineer · London, UK
Profile
Product and infrastructure engineer with three years of startup experience owning systems from architecture through production. Recent work spans AI products used by thousands, low-latency media over object storage, and reliable webhook infrastructure.
Software engineer with three years of startup experience building product infrastructure and performance-sensitive systems. Recent work spans distributed coordination, LL-HLS/CMAF media over object storage, reliable webhook delivery, and privacy-sensitive identity tooling.
Product and backend engineer with three years of startup experience owning TypeScript, Python, Ruby, and PostgreSQL systems from ambiguous requirements through production. Built and operated products used by 4,400+ students across 104 countries.
Product and infrastructure engineer with three years of startup experience building applied-AI products and agent-assisted development workflows. I design the architecture, specifications, and review loops behind systems spanning webhooks, browser automation, and distributed media.
Software engineer with experience across Swift/Core NFC, privacy-sensitive identity tooling, and backend infrastructure. Published an on-device ICAO 9303 document reader and extended an open-source Swift package for secure NFC travel-document access.
Experience
- 2025–2026
Founding Software Engineer — Built university discovery and a fine-tuned AI statement reviewer for international applicants, used by 4,400+ students in 104 countries.
- Owned the product end to end across TypeScript, PostgreSQL, Cloudflare Workers, Durable Objects, R2, data pipelines, AI services, analytics, and internal tools.
- Built an iterative personal-statement reviewer fine-tuned across five model versions on expert feedback; delivered 3,100+ reviews and nearly 23,000 span-anchored comments.
- Built a PostgreSQL ranking engine over 50,000+ UCAS courses using around 25 filters and signals, and migrated the platform from Next.js/Vercel to TanStack Start/Cloudflare Workers.
- Ran the reviewer as a queue-backed Workers and Durable Objects service to absorb deadline-driven bursts, with PostgreSQL behind Hyperdrive and R2 for storage.
- Turned reviewers' Google Docs comments into fine-tuning data and evaluated each model version directly with the experts whose judgement it was learning.
- 2023–2025
Software Engineer — Built and ran course discovery and human-reviewed AI statement feedback for UK university applicants as the sole engineer.
- Owned seven Next.js frontends, a Python/Flask API on AWS Lambda, SQL Server data pipelines, AI workers, transactional email, and internal operations tooling.
- Built a three-pass GPT-4 review pipeline and a from-scratch annotation dashboard, enabling human reviewers to refine span-anchored feedback across 600+ statements and 5,100+ inline comments.
- Operated the platform through a full admissions cycle and into 2025, adding Sentry and PostHog observability and simplifying eight deployments into a single Next.js/Supabase application.
- Diagnosed a silent review-notification failure, resent every affected result, and isolated transactional email behind a smaller service so the same failure could not remain hidden.
Selected Engineering Work
- 2026
A Rails/PostgreSQL gateway for verifying, transforming, and reliably delivering webhooks. hookrail.dev
- Built and deployed a Rails 8.1/PostgreSQL gateway with Solid Queue, Hotwire, and a Rust CLI, covering signature verification, filtering, transformations, deduplication, configurable retries, and local delivery.
- Designed the architecture, retry and concurrency semantics, and security boundaries; specified bounded work in PRDs, reviewed every diff, and backed the service with 60 test files plus CodeQL, Brakeman, and bundler-audit.
- Implemented provider-configurable HMAC verification, idempotent deduplication, sandboxed JavaScript transforms, per-connection retry policies, guarded health transitions, signed outbound delivery, and a local Rust tunnel.
- Converted the product into testable PRD slices, delegated bounded implementation work to parallel AI agents, and reviewed every diff for specification conformance, correctness, scope, and interface-seam drift.
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A draft protocol and reference implementation for low-latency live media over object storage.
- Built an OBS-to-browser LL-HLS reference deployment using RTMP/ffmpeg, CMAF, Cloudflare Workers, Durable Objects, and R2, reaching roughly 4–4.5 seconds end to end.
- Designed media-agnostic commit semantics around immutable objects, idempotent commits, a compare-and-set forward-only cursor, contiguous-prefix ordering, recovery, and bounded retention.
- Benchmarked the isolated coordinator path over 1,000 real H.264 parts at roughly 1.2 ms median commit-and-wake overhead, with about 126 ms median end-to-end latency in the local harness.
- 2026
A local-first browser extension that learns repeated workflows and replays them without sending browsing data to a server.
- Built a TypeScript browser extension that records clicks, input changes, and submissions, mines repeated flows on-device, and AES-GCM encrypts saved activity before storage.
- Persisted run state across service-worker restarts and designed replay to pause rather than guess when an element, secret, CAPTCHA, or page state prevents safe progress.
- 2026
An email-native service that turns image attachments into a PDF and replies in the same thread.
- Built a Cloudflare Workers pipeline that parses MIME email, validates untrusted attachments by file contents, normalises EXIF orientation, strips metadata, generates mixed-orientation PDFs, and replies with the result.
- Added Stripe-backed billing without a dashboard, signature-verified webhooks, early rate limits, thread-level deduplication, and defences against mail loops, spoofing, and attachment bombs.
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On-device Swift tooling for reading ICAO 9303 passports and identity cards over Core NFC. github.com/arsenstorm/MRTDReader
- Published an App Store app that scans MRZ data and reads compatible NFC document chips entirely on device without storing or sharing document data.
- Forked and extended NFCPassportReader into MRTDReader, a Swift package supporting multiple MRTD formats, BAC, secure messaging, passive and active authentication, chip authentication, and PACE.
- 2026
A multi-model workspace for comparing and evaluating AI outputs.
- Built parallel streaming across multiple model providers, per-model parameter controls, stored prompt history, and judge-model evaluation in one comparison workspace.
- 2025
A Rust CLI that explains how to install a missing command instead of failing opaquely.
- Published a cross-platform Rust CLI that detects missing dependencies, returns operating-system-specific installation guidance, and supports project-defined overrides.
- 2024
A search and trend platform indexing more than 50 million Amazon keywords.
- Built keyword search, ranking history, ASIN tracking, category-trend detection, and API/MCP access over a large marketplace dataset.
Technical Writing
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PRDs, agents and review loops for a production service.
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What if browser automation didn't need a script?
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What if live video could be streamed from object storage?
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What if you built a SaaS product without a website?
Skills
- Languages: TypeScript/JavaScript, Python, Ruby, Rust, Swift, SQL
- Backend and data: PostgreSQL, Rails, Flask, Cloudflare Workers, Durable Objects, R2, AWS Lambda, Supabase
- Frontend: React, Next.js, TanStack Start, Hotwire, Tailwind CSS
- Languages: TypeScript, Rust, Python, Ruby, Swift, SQL
- Systems: Distributed coordination, object storage, HTTP/webhooks, LL-HLS/CMAF, RTMP/ffmpeg, Core NFC/ICAO 9303
- Infrastructure: Cloudflare Workers, Durable Objects, R2, PostgreSQL, AWS Lambda, GitHub Actions
- Languages: TypeScript, Python, Ruby, Rust, SQL
- AI: Fine-tuning data pipelines, iterative model evaluation, multi-pass LLM systems, agent-assisted development
- Backend: PostgreSQL, Cloudflare Workers, Durable Objects, Rails, Flask
- Languages: Swift, Rust, TypeScript, SQL
- iOS and identity: Core NFC, ICAO 9303, BAC, PACE, secure messaging, document authentication
- Backend and security: Rails, webhooks, PostgreSQL, Cloudflare Workers, data minimisation
Education
- 2023—2026
BSc (Hons) Computer Science (Artificial Intelligence)
University of Greenwich · First Class Honours