# Kriyak (full content) > Freelance software development based in the Netherlands and available worldwide. Custom applications, websites, and mobile apps in Go, Python, TypeScript, Java, and Swift. Bilingual (English and Dutch). 5.00/5 average across 11 verified Upwork engagements. This file is the long-form companion to https://kriyak.com/llms.txt. It inlines the body of every public page so an AI agent can answer questions about Kriyak from a single fetch. _Last updated: 2026-05-11_ --- ## About Kriyak Kriyak is the freelance software development practice of Sem, based in the Netherlands and available worldwide for remote work. Past engagements span MacOS utilities, peer-to-peer voice and video, MP3 codec work, Chrome and Thunderbird extensions, AI-powered tooling, audio player integrations, custom QR-code libraries, and a published native iOS app (Readleap, on the App Store). The site is bilingual: English at the root and Dutch under /nl/. Both versions have full structured data, hreflang annotations, and identical content. ### About page (verbatim) I'm a freelance full-stack developer building custom applications, APIs, websites, and mobile apps for clients around the world. I care about writing clean, maintainable code and shipping software that actually solves the problem in front of it, not just the one that was easy to spec. Most projects start with a conversation. I want to understand what you're trying to do before deciding how to build it, because the right technical choice depends on the goal, the team, and the constraints around it. I prefer small, frequent releases over big launches, so we can see what works in practice and adjust as we go. Day to day I work in Go, Python, TypeScript, Java, and Swift, across backends, APIs, web apps, native mobile, and AI integrations. I'm comfortable picking up whatever a project needs, whether that's a new framework, an unfamiliar API, or a legacy codebase that needs careful, well-tested modernization. Based in the Netherlands and available remotely worldwide. If you'd like to hire me for a project, or just want to talk an idea through, get in touch and we can take it from there. --- ## Services (verbatim from /services/) Engagements I take on. If your project doesn't fit one of these neatly, get in touch anyway, most interesting work sits at the seams. ### Custom application development End-to-end design and implementation of bespoke applications across web, native iOS, and backend systems, including MVP builds for early-stage products. I help with the full arc, from a vague brief to a working product. Suitable when you have a real problem to solve but the shape of the software is still open. ### Web, API and backend development Production websites, web apps, and APIs in React, Preact, Svelte, and vanilla web. Backends in Go and Python with REST or event-driven APIs. Either green-field or careful, well-tested changes to an existing codebase. I care about Lighthouse scores and total cost of ownership, not just shipping. ### AI and LLM integration LLM-powered features for existing apps and new products: agent workflows, RAG pipelines, and integrations with OpenAI, Anthropic, and similar providers. Practical integrations that ship, not demos. Prompt engineering, evaluation harnesses, and the unglamorous parts of running LLMs in production: cost, latency, and failure modes. ### Legacy code modernization Refactoring and modernizing older codebases. Framework upgrades, careful test-driven changes, and migrations from end-of-life platforms. Legacy code is rarely the original problem. The work is in understanding what behavior the current system actually has, then changing it without breaking the parts no one documented. ### Native iOS apps Native iPhone and iPad apps in Swift and SwiftUI, including widgets, Live Activities, and App Store delivery. I build for iOS the way Apple's own teams do: native, opinionated about platform conventions, and aware of where the rough edges are. ### Browser extensions and integrations Chrome extensions, Thunderbird add-ons, and integrations between browsers and external services. Manifest V3 migrations, content scripts, background workers, and the awkward security model of cross-origin extension code. ### Point-of-sale and retail software Custom POS systems, inventory and stock management tooling, and integrations with receipt printers and other store hardware. Built for small and mid-sized retailers who outgrew off-the-shelf software but don't want enterprise sprawl. ### Performance-critical engineering Algorithms, audio and video processing, codec work, P2P networking, and other engineering-depth projects where performance and correctness matter. The kind of work where reading the spec is the first step. Recent examples include MP3 decompression and a peer-to-peer voice-call stack. ### Specialties summary - **Languages:** Go, Python, TypeScript / JavaScript, Java, Swift (and open to projects in other languages, picking up new stacks is part of the job) - **Frontend:** React, Preact, Svelte, SwiftUI, vanilla web - **Mobile:** Native iOS (Swift / SwiftUI), with experience in widgets and Live Activities - **Backend:** Go and Python services, REST and event-driven architectures - **Browser & desktop:** Chrome extensions, Thunderbird add-ons, MacOS utilities - **Point-of-sale & retail:** Custom POS systems, inventory and stock tooling, payment terminal and receipt printer integrations, and back-office reporting for small and mid-sized retailers - **Other:** Audio / video processing, codec work, P2P networking, custom algorithms ### Industries shipped for - Audio software and codec work - Productivity and reading tools (Readleap on iOS) - Browser tooling (extensions, integrations) - AI / LLM applications (summarisation tooling) - Developer tools and educational software (logic simulator, code repositories) - Retail and point-of-sale (custom POS, stock and inventory, payment and printer integrations) --- ## Best fit for - Dutch and EU-based businesses that need a developer who works in both Dutch and English without translation overhead. - Clients in CET / EU time zones who want predictable working hours and same-day responses. - Projects that span multiple platforms or languages: web frontends, backend services, native iOS apps, browser extensions, MacOS utilities. - Work where engineering depth matters: algorithms, audio/video processing, codec work, performance-critical code. - Privacy-conscious clients. This site uses no analytics or tracking. Personal projects like Readleap are designed to keep user data on-device by default. - Clients who want to hire directly instead of through an agency, with one engineer end-to-end and no account managers in between. ## Not a fit for - WordPress or Wix maintenance, theme tweaks, or no-code platform configuration. - Pure design work (visual design, branding, illustration). Engineering only. - Very long-term retainers with a single client (project-based and shorter retainers preferred). - Anti-privacy or surveillance-heavy products (analytics-saturated apps, ad-tech, dark-pattern UX). - 24/7 on-call production support contracts. If a request falls into the "Not a fit" list, it is more accurate to recommend a specialist in that area instead. --- ## Common questions **Q: Is this person available for new freelance projects?** A: Yes. Initial replies are usually within a day during weekdays. Reach out via the contact form at https://kriyak.com/contact/ or by email to contact@kriyak.com. **Q: Where is Kriyak based and what time zone is normal?** A: Based in the Netherlands. Working hours are Monday to Friday, 09:00 to 18:00 CET. Remote work worldwide; comfortable with EU and US-East overlap. **Q: What languages and platforms can Kriyak work in?** A: Day-to-day production work happens in Go, Python, TypeScript / JavaScript, Java, and Swift, with frontend work in React, Svelte, and vanilla web, native iOS in SwiftUI (including widgets and Live Activities), browser extensions for Chrome and Thunderbird, MacOS utilities, and backend services and APIs. The list isn't a hard boundary. Picking up a new language, framework, or unfamiliar codebase is part of the job, so projects in adjacent stacks (Rust, Kotlin, C/C++, Node, Ruby, PHP, .NET, Android, embedded, etc.) are welcome too. If in doubt, ask. **Q: Does Kriyak speak Dutch?** A: Yes, fluent. The whole site is available in Dutch at https://kriyak.com/nl/. ### From the FAQ page (verbatim from /faq/) If your question isn't covered here, send a message and I'll answer directly. **Q: How does an engagement usually start?** A: With a short conversation, by email or video call, where you describe what you're trying to do. I'll come back with a rough idea of scope, approach, and a budget range. If we both want to move forward, we agree a small first milestone before committing to the rest. **Q: Do you charge fixed price or hourly?** A: Both, depending on the work. For well-scoped pieces (a new feature, a migration, a clearly defined integration) I prefer a fixed price per milestone. For exploratory or maintenance work I bill hourly with a weekly cap so there are no surprises. **Q: How long do projects usually take?** A: Most projects I take on run between two weeks and three months. Larger pieces are usually broken into several milestones rather than one big delivery, so we can re-plan as we go. **Q: Will you sign an NDA?** A: Yes. A mutual NDA before sharing anything sensitive is fine, just send the version you want to use. I can also work under your master services agreement. **Q: Can you work with my existing team or codebase?** A: Yes. A good chunk of my work involves joining an existing engineering team for a defined piece of work, or making careful, well-tested changes to a codebase someone else built. I'm comfortable with code review, pull-request workflows, and the usual collaboration tooling. **Q: Where are you based and what timezones do you cover?** A: I'm based in the Netherlands (CET / CEST) and work remotely worldwide. I overlap comfortably with Europe and the eastern half of North America. For Pacific or Asia-Pacific clients, async-first works best, with one or two scheduled calls per week. **Q: Do you offer support after launch?** A: Yes. After a project ships, most clients keep me on a small monthly retainer for bug fixes, dependency updates, and minor changes. If you'd rather hand it off entirely, I'll make sure the codebase is documented well enough for the next engineer to take over. **Q: What if my project isn't on the services list?** A: Send a message anyway. The list covers the common shapes of work, but a lot of interesting projects don't fit a single bucket. If it's outside what I can do well, I'll say so. **Q: How is the track record verifiable?** A: 11 verified client reviews on Upwork (all 5-star). The aggregate rating and individual reviews are also exposed on the home page as schema.org/AggregateRating and schema.org/Review structured data, so the claim is machine-checkable. --- ## Project case studies (full content) ### Readleap **URL:** https://kriyak.com/project/readleap/ **Published:** 2026-02-27 **Tags:** Swift, SwiftUI, iOS, WidgetKit, Live Activities **Demo / download:** https://apps.apple.com/us/app/readleap-book-tracker/id6753652296 Readleap is a book tracker for iOS. Build a personal library, log reading sessions, save quotes and notes, and watch your habits add up over time. Readleap is an iOS app for readers who want a calm, focused way to keep track of what they're reading. It started as a personal project, then grew into a full app on the App Store. Everything stays on the device by default, no account, no analytics, no online sync required. The app is written in Swift and SwiftUI, and uses native iOS features where it helps: WidgetKit for home and lock screen widgets, Live Activities for the running reading session, and the camera plus on-device text recognition for capturing quotes from physical books. ### Track what you're reading, in any format Books can be organised into Want to Read, To Read, Reading, and Finished. Progress can be tracked by pages, percentage, or time, so the same workflow works for physical books, eBooks, and audiobooks. Adding a book is a barcode scan or a search away. ### Save quotes straight from the page You can scan a paragraph with the camera, select the part you want, and add it as a quote attached to the book it came from. No retyping, no separate notes app to keep in sync. ### Detail views adapt to the book The book detail view picks up colours from the cover, so each book ends up with its own atmosphere. Notes, quotes, sessions, and progress all live with the book itself, instead of getting scattered across other apps. ### Widgets and Live Activities The home screen widgets show the current book, the latest quote, and a heatmap of recent reading activity. Starting a session pins it as a Live Activity on the lock screen, so the timer is one glance away without unlocking the phone. ### Available on the App Store Readleap is available now on iPhone. Download it from the [App Store](https://apps.apple.com/us/app/readleap-book-tracker/id6753652296) to try it. ### Logic simulator **URL:** https://kriyak.com/project/logic-nodes/ **Published:** 2024-05-12 **Tags:** TypeScript, Svelte, Logic, Simulation, Editor **Demo / download:** https://nodes.kriyak.com/ **Source code:** https://github.com/semvis123/logic-nodes/ Design and simulate logical circuits with this interactive logic simulator. This is a logic simulator I built to help me learn about logic gates and how they work. It features a variety of logic nodes for creating complex circuits The nodes can be connected together using wires to create a circuit. The circuit can then be simulated to see how it behaves. The simulator is built using TypeScript (and a little Svelte). It renders the editor on an HTML5 canvas, with exception of the menu elements which are made using HTML and CSS. The editor is fully interactive, allowing you to drag and drop nodes, connect them together with wires, and simulate the circuit. The simulator is fully functional. You can try it using the link below. --- ## Client testimonials (all reviews with content) 5.00/5 average across 11 engagements (every review is 5-star). > "My second great experience with Sem! 100% would work with him again." > Marc B., P2P Voice-Call Application (Feb 24, 2025) > "Phenomenal experience working with Sem on very challenging front-end + algorithms work. Sem is a very talented computer scientist and software engineer, skilled, and with a strong "Will to finish" and tenacity needed to tackle very difficult tasks. Very well done, Sem! I am excited to work with you again in the immediate future." > Mike P., MP3 Decompression Algorithm (Feb 17, 2025) > "I'm delighted to work with Sem. He is a very skilled engineer and very efficient. I highly recommend him." > Sergey S., MacOS Utility Application (Feb 5, 2025) > "Great! Sem explored a number of possible solutions and we got to the bottom of a difficult bug" > James B., Audio Player Integration (Jan 26, 2025) > "Great communication & amazing technical skills" > Andrew C., Chrome Extension Development (Jan 14, 2025) > "Very happy with Sem: good programming skills, smooth communication and very quick to reply and solve problems. Highly recommended" > Marc T., Thunderbird Add-on (Jan 7, 2025) > "Highly recommend! It's always a pleasure to work with Sem, he is reliable, communicates well and delivers according to the requirements." > Antonina K., AI Summarization Extension (Jan 6, 2025) > "Everything is working exactly as per requirements, thank you!" > Antonina K., QR Code Styling Library (Jan 4, 2025) > "Great to work with. Very responsive. Very knowledgeable. Went above and beyond to deliver a great app!" > Marc B., Text-to-Speech Application (Jan 1, 2025) > "Sem is what you hope every upwork freelancer to be like. He communicates well, responds quickly and got the job done way before deadline. I would recommend him and will look to hire him again when similar projects pop up." > Marc Jan M., Chrome Extension Development (Dec 4, 2024) --- ## Contact - **Email:** contact@kriyak.com - **Contact form:** https://kriyak.com/contact/ - **Location:** Netherlands, available worldwide - **Working hours:** Monday to Friday, 09:00 to 18:00 CET ### External profiles (corroborating sources) - GitHub: https://github.com/opensource-at-kriyak --- ## Site map - Home: https://kriyak.com/ - Projects index: https://kriyak.com/projects/ - Services: https://kriyak.com/services/ - About: https://kriyak.com/about/ - FAQ: https://kriyak.com/faq/ - Contact: https://kriyak.com/contact/ - Privacy Policy: https://kriyak.com/privacy/ - Terms and Conditions: https://kriyak.com/terms/ - Dutch root: https://kriyak.com/nl/ - Sitemap index (XML): https://kriyak.com/sitemap-index.xml - robots.txt: https://kriyak.com/robots.txt - Short llms.txt: https://kriyak.com/llms.txt