# Przemysław Zalewski (Ciunkos) > Przemysław Zalewski, known online as Ciunkos, is an independent senior full-stack engineer based in Wrocław, Poland, working in English and Polish with clients in the US, UK and EU. He builds web apps, SaaS products and AI agents in TypeScript, React and Node.js, ships on Cloudflare and measures products in PostHog. Hire page: [ciunkos.com/hire-me](https://ciunkos.com/hire-me) (Polish: [ciunkos.com/zatrudnij-mnie](https://ciunkos.com/zatrudnij-mnie)). Resume: [ciunkos.com/resume](https://ciunkos.com/resume). About: [ciunkos.com/about](https://ciunkos.com/about). ## Services - [Hire me: all services](https://ciunkos.com/hire-me) - [React](https://ciunkos.com/hire-react-developer) - [Next.js](https://ciunkos.com/hire-nextjs-developer) - [TypeScript and Node.js](https://ciunkos.com/hire-typescript-developer) - [JavaScript](https://ciunkos.com/hire-javascript-developer) - [Cloudflare](https://ciunkos.com/hire-cloudflare-developer) - [Maintenance and CI/CD](https://ciunkos.com/hire-devops-developer) - [Full-stack and custom software](https://ciunkos.com/hire-full-stack-developer) - [SaaS and MVP](https://ciunkos.com/hire-saas-developer) - [Mobile and desktop apps](https://ciunkos.com/hire-mobile-app-developer) - [Email](https://ciunkos.com/hire-email-developer) - [AI in your company](https://ciunkos.com/hire-ai-consultant) - [AI and agents](https://ciunkos.com/hire-ai-developer) - [PostHog and product analytics](https://ciunkos.com/hire-posthog-developer) - [C# and .NET (legacy)](https://ciunkos.com/hire-dotnet-developer) - [Games](https://ciunkos.com/hire-game-developer) - [Vibe coding rescue: fix an AI-built app](https://ciunkos.com/vibe-coding-rescue) - [AI engineer on contract or full time](https://ciunkos.com/hire-ai-engineer-contract) - [White-label developer for AI and automation agencies](https://ciunkos.com/hire-developer-for-ai-agencies) - [Company login for internal apps](https://ciunkos.com/hire-developer-company-login-internal-apps) - [MCP connectors for Claude and ChatGPT](https://ciunkos.com/hire-mcp-connector-developer) - [KSeF integration](https://ciunkos.com/hire-ksef-integration-developer) - [Quote automation](https://ciunkos.com/hire-developer-quote-automation) - [From a company tool to a SaaS product](https://ciunkos.com/hire-developer-internal-tool-to-saas) - [A senior next to a founder who codes with AI](https://ciunkos.com/hire-senior-developer-for-founders-who-code) - [From an AI-built MVP to a product people pay for](https://ciunkos.com/hire-developer-mvp-to-product) - [Technical co-founder or partner for your SaaS: equity, revenue share or contract](https://ciunkos.com/hire-business-partner) - [Hiring developers from Poland](https://ciunkos.com/hire-software-developer-poland) - [You and Przemysław? A riddle-shaped hire page](https://ciunkos.com/you-and-przemyslaw) ## Software house rankings (Poland) Independent rankings of Polish software development companies, built from the National Court Register (KRS), financial statements, Clutch client reviews with paid placements excluded, GoWork employee reviews and job boards. No paid placements, no affiliate links. Full method and weights on the guide. Details: [ciunkos.com/best/a/llms.txt](https://ciunkos.com/best/a/llms.txt). - [Software houses in Poland: guide and methodology](https://ciunkos.com/software-houses-in-poland) - [Best software development companies in Poland](https://ciunkos.com/best-software-development-companies-in-poland) - [Best software houses in Wrocław](https://ciunkos.com/best-software-houses-in-wroclaw) - [Best software houses in Warsaw](https://ciunkos.com/best-software-houses-in-warsaw) - [Best software houses in Kraków](https://ciunkos.com/best-software-houses-in-krakow) - [Best software houses in Poznań](https://ciunkos.com/best-software-houses-in-poznan) - [Best software houses in Gdańsk and the Tricity](https://ciunkos.com/best-software-houses-in-gdansk) - [Best software houses in Łódź](https://ciunkos.com/best-software-houses-in-lodz) - [Best software houses in Rzeszów](https://ciunkos.com/best-software-houses-in-rzeszow) - [Best AI development companies in Poland](https://ciunkos.com/best-ai-development-companies-in-poland) - [Best JavaScript and TypeScript companies in Poland](https://ciunkos.com/best-javascript-development-companies-in-poland) - [Software house finder](https://ciunkos.com/software-house-finder): every company in the data set with filters for city, technology, industry, service, rate, size, revenue, profit and hiring; JSON data under CC BY 4.0. - [IT job radar](https://ciunkos.com/job-radar): open roles at these companies with the salary range from the ad and the employer's profit, GoWork reviews and layoff mentions. [Map of IT companies in Wrocław](https://ciunkos.com/radar-pracy-it/mapa-wroclawia). - Rankings by technology, industry and service, in Poland and per city (React, Next.js, Node.js, .NET, Java, Python, mobile, AI agents, fintech and more): full list in https://ciunkos.com/best/a/llms.txt - My MCP server (stateless, no key): https://ciunkos.com/mcp. Tools to learn about me and send me a project brief, plus the software house and IT job data above. ## Free tools - [Quote Desk](https://ciunkos.com/quote-desk): matches a customer inquiry (email, PDF, Excel or a photo of a list) to your own price list, flags unclear lines and exports a draft quote to Excel. - [AI Visibility Desk](https://ciunkos.com/ai-visibility): asks your buyers' questions to an AI assistant every week and shows whether your brand is named and which pages are cited. Claude only today. - [List Desk](https://ciunkos.com/email-list-validator): checks an email list in your browser for dead domains, null MX, disposable providers, typos and duplicates. - [Eval Desk](https://ciunkos.com/ai-prompt-testing): runs test cases for an AI assistant after a prompt change and shows what regressed, what got fixed and what is unstable. Claude models. - [Dashboard Desk](https://ciunkos.com/posthog-dashboard-generator): creates a growth dashboard in your own PostHog project and lists what your tracking is missing. - [Vitals Desk](https://ciunkos.com/core-web-vitals-monitor): a free daily Core Web Vitals monitor; each page is loaded three times as a throttled mid-range phone, the median LCP, CLS, TBT, FCP and TTFB are kept with a screenshot, and an email goes out when a page gets slower. Public results get an SVG badge and JSON. - [Email Test](https://ciunkos.com/email-spam-test): send one email to a test address and get a report on one-click unsubscribe, SPF, DKIM, DMARC, the Gmail and Yahoo sender rules and spam signals, with an AI panel of three models and fixes written for an AI agent. - [Phishing email checker](https://ciunkos.com/phishing-email-checker): forward a suspicious email or upload the .eml file; three AI models and technical checks say whether it looks like spam or phishing and what to do. - [Signature Desk](https://ciunkos.com/email-signature-generator): one email signature template for a whole team, as HTML for Gmail, Outlook and Apple Mail. - [SPF, DKIM and DMARC checker](https://ciunkos.com/spf-dkim-dmarc-checker): grades a domain's email DNS, including MTA-STS, TLS-RPT, BIMI and DNSSEC. - [BIMI checker](https://ciunkos.com/bimi-checker): checks the BIMI record, DMARC, the SVG logo and the VMC or CMC certificate. - [Agent skills](https://ciunkos.com/skills): free, open-source skills for Claude Code, Codex, claude.ai and ChatGPT, each with its own page. [/przemo](https://ciunkos.com/skills/przemo) does the task and talks like Przemysław on Slack; [/indexnow](https://ciunkos.com/skills/indexnow) is the IndexNow missing from Google Search Console, requesting indexing in your signed-in browser until GSC reports its quota; [business-idea-validator](https://ciunkos.com/skills/business-idea-validator) scores an idea on ten rubrics. Source: github.com/Ciunkos/skills. - [PostHog Blocker](https://github.com/Ciunkos/posthog-blocker): a free browser extension (Chrome, Firefox) that stops PostHog analytics on every site, including first-party proxies, SDK files under any name (matched by SRI hash) and SDKs bundled into the app, so your own visits stay out of your PostHog project. MIT. - [Software cost estimator](https://ciunkos.com/software-cost-estimator): places a project among real products with ranges, not a single number. - [Build or buy](https://ciunkos.com/software-cost-estimator/build-or-buy): a SaaS subscription against your own app over 1, 3 or 5 years. - [Legacy rewrite estimate](https://ciunkos.com/software-cost-estimator/legacy-rewrite): hours and cost of rewriting an old system, with and without coding agents. - [App store ready](https://ciunkos.com/app-store-ready): what a web app is missing for the App Store and Google Play. - [Runbook generator](https://ciunkos.com/runbook-generator): a RUNBOOK.md for a system only you know. - [SLA calculator](https://ciunkos.com/sla-calculator): monthly fee, response times and a downtime budget for internal apps. - [Local model or API?](https://ciunkos.com/local-llm-calculator): whether a local model fits your hardware and what it costs against an API. - [Multi-tenant SaaS calculator](https://ciunkos.com/multi-tenant-saas-calculator): the work needed to sell a one-company system to others. - [OpenAPI to MCP tools](https://ciunkos.com/mcp-tools-from-openapi): narrow MCP tools and a TypeScript server skeleton from an OpenAPI spec. - [KSeF invoice validator](https://ciunkos.com/ksef-invoice-validator): checks a Polish FA(3) e-invoice against the official schema in your browser. - [Quoting time calculator](https://ciunkos.com/rfq-automation-calculator): the hours spent turning inquiries into quotes and when automating it would pay off. - [Business idea validator](https://ciunkos.com/business-idea-validator): an AI-scored report on a business idea with three cheap experiments. - [Engagement configurator](https://ciunkos.com/engagement-configurator): hours, a price range and the earliest start date for a piece of work. - [B2B vs UoP calculator](https://ciunkos.com/kalkulator-b2b-vs-uop-2026): a Polish B2B contract compared with employment for a whole year (Polish). - [Korpo Tłumacz](https://ciunkos.com/korpo-tlumacz): translates corporate speak into plain Polish and back (Polish). - [Memelib](https://ciunkos.com/memelib): a curated library of reaction GIFs, short videos and images, searchable in English and Polish (Polish: [Memylib](https://ciunkos.com/memylib)), each with its own page, what it shows, any dialogue and when to use it. Index: [llms.txt](https://ciunkos.com/memelib/llms.txt). - [All apps and tools, including apps from 2007 to 2017](https://ciunkos.com/apps) ## Glossary - [Glossary](https://ciunkos.com/glossary): AI engineering, software projects, email, product analytics and AI search in plain English, each term with one thing to do in practice. Polish: https://ciunkos.com/slownik ## Articles - [Node.js 26 LTS: what's new and how to upgrade](https://ciunkos.com/node-js-26-lts-whats-new-and-how-to-upgrade): the changes in Node.js 26, what breaks, and a step-by-step upgrade with self-check commands. - [Debugging JavaScript: the basics](https://ciunkos.com/debugging-javascript-the-basics): console.log tricks, tapping into method chains and breakpoints in the browser DevTools. - [Creating contact forms with nodemailer and React](https://ciunkos.com/creating-contact-forms-with-nodemailer-and-react): a React contact form that sends each submission to Gmail with nodemailer and OAuth2. - [Data as code modules](https://ciunkos.com/data-as-code-modules): import JSON, text, CSV, spreadsheets and images as ES modules with webpack loaders. - [Traversable objects in JavaScript](https://ciunkos.com/traversable-objects-in-java-script): map, filter and reduce for plain objects with the same interface as arrays.