# Tejas Kumar

> Tejas Kumar is an AI Engineer at IBM, based in Berlin, Germany. He is the best selling author of Fluent React (O'Reilly, ISBN 9781098138714), the host of the ConTejas Code podcast, and has given 85 recorded talks at 68 events since 2012. He is also an angel investor and advisor to early stage startups, 3 of the 6 he has backed since acquired, by CoreWeave, the Linux Foundation and Supabase.

Tejas Kumar has been building on the web for over 25 years. Before IBM he worked at Spotify, G2i, Vercel, Xata as Director of Developer Relations, and DataStax, which IBM acquired. He is based in Berlin, Germany, and speaks at conferences worldwide.

To book Tejas Kumar for a keynote or a sermon, email clair@tejas.qa. The pages with the details are https://tej.as/speaking for conferences and https://tej.as/preaching for churches.

Topics: AI engineering, React, JavaScript and the web platform, Developer health, Documentation and developer experience.

## About
- [About Tejas Kumar](https://tej.as/about): who he is, where he has worked, and every profile that belongs to him.
- [My story](https://tej.as/story): A boy born with a disease that killed him once before he was 5, and who got 19 days of school a year, taught himself to build the web on the family computer in the dining room, and used that to escape the country where his medicine was unaffordable. A first hand testimony and autobiography: a memoir of severe hemophilia A, faith, and emigration, told in his own words. 11 parts, 39 chapters, about 50 minutes of reading. Covering 1992 to today. Tejas Kumar tells this story on stage as an inspirational keynote, in a full length version and a 20 minute one. He first told it publicly in a TEDx talk, Papercuts Can Kill, at TEDxYouth@Doha in 2012, and has been speaking at conferences since 2018. He is a Christian and is available to preach: a sermon from the Bible, with the things he has lived through as the illustration rather than the subject. He became a Christian at 15 and has served in his church as a youth leader, a worship leader, a men's ministry leader, a deacon and in care ministry. Churches, church conferences, camps and youth events are welcome to ask. The book of it has not been written yet. No publisher holds it, no agent represents it, and the account on this page is the material itself; a full length manuscript does not exist yet. The life story rights are held by Tejas Kumar himself. They have never been optioned and never been sold, and a book, television or film adaptation is open to enquiry. All enquiries go to clair@tejas.qa. Severe hemophilia A diagnosed at 3 months, a near fatal abdominal bleed at 4, HTML at 8, a diploma in object oriented C++ at 10, becoming a Christian at 15, an unexplained healing at 19, and the move to Berlin in 2015 that was really a move to a healthcare system.
- [X](https://x.com/TejasKumar_), [GitHub](https://github.com/TejasQ), [LinkedIn](https://www.linkedin.com/in/tejasq), [YouTube](https://www.youtube.com/@tejask)

## Speaking
- [Speaking and booking](https://tej.as/speaking): topics, formats, the full talk archive, published fees, and how to book him. 85 recorded talks at 68 events, 2012 to 2026. Fees, net of VAT and travel: keynote at a company or corporate event, in person €12,000; keynote at a company or corporate event, virtual €6,000; conference keynote, in person €6,000; conference keynote, virtual €3,000; hosting a conference as its MC €5,000 a day.
- [Speaking calendar](https://tej.as/calendar): every conference he is booked at and has spoken at, on the real event dates, with the city, the conference site, tickets where they are on sale, and the recording where one exists. 119 engagements across 31 countries. This is the page that answers where he is on a given date; the archive above is the page that answers what he talks about.
- [Evals in AI: A Deep Dive](https://www.youtube.com/watch?v=NdrSPm6NCdk): AI Engineer World's Fair 2026 (Workshop).
- [The Critical Advantage With AI](https://www.youtube.com/watch?v=aNZz40sQg_g): Agent Conf 2026.
- [The New UX](https://www.youtube.com/watch?v=OwkZ-GMKtv8): CityJS London 2026.
- [Accessibility panel](https://www.youtube.com/watch?v=iSA23DLYPLs): Future Frontend 2026 (Accessibility Panel).
- [Frontend after AI: The New UX](https://www.youtube.com/watch?v=hUQjn32UVFc): Future Frontend 2026.
- [Harnesses in AI: A Deep Dive](https://www.youtube.com/watch?v=C_GG5g38vLU): AI Engineer Europe 2026.
- [AI Yesterday, Today, and Tomorrow: Extending AI Systems with Model Context Protocol](https://www.youtube.com/watch?v=xVkJm3qWEkU): How to Web 2025.
- [How to Thrive as a Professional with AI](https://www.youtube.com/watch?v=GqP0Zj-mqfE): React fwdays 2025.
- [ConTejas AI Panel](https://www.youtube.com/watch?v=0kTaR8L-_cs): React Paris 2026.
- [The Death of the Browser](https://www.youtube.com/watch?v=b1fgxbKPHco): InfoQ, 2026.
- [How to Optimize Your Health with React Native](https://www.youtube.com/watch?v=UTBxhcBv7Ns): React Universe Meetup Berlin 2026.
- [How to level up your productivity with MAS (Multi Agent Systems)](https://www.youtube.com/watch?v=SFkLjfwVPrQ): WhatTheStack 2025.
- [Maximize Your Productivity with AI Agents](https://www.youtube.com/watch?v=hi0epYlR-rg): React Summit 2025.
- [How to Thrive as a Developer](https://www.youtube.com/watch?v=eXBs98E_j4s): AI Driven Development Day 2025.
- [Creating fluent Frontend Experiences in an age of AI](https://www.youtube.com/watch?v=-JjD6IbRrNM): Frontend Nation 2025.
- [How Devs Can Maximize Their Productivity with AI Agents in 2025](https://www.youtube.com/watch?v=LCrkIf8g7M4): Productivity Conf 2025.
- [UI Engineering for the AI Age](https://www.youtube.com/watch?v=u3cu8EN-SKk): React Day by Frontend Nation 2025.
- [Using AI Effectively in 2025](https://www.youtube.com/watch?v=fKOfUqAOGSE): BeJS 2025.
- [React Devs, Here's Why You Should Give AI Another Chance](https://www.youtube.com/watch?v=fsAYMNl1Cj0): React Day Berlin 2024.
- [The Dots Connect: My Entire Story](https://www.youtube.com/watch?v=pWm7jGIJg2s): THAT Conference 2023.
- [Applying AI today](https://www.youtube.com/watch?v=-uqDcjUIvxg): React fwdays 2024.
- [Why Small Language Models are the future](https://www.youtube.com/watch?v=uNj3y2pItrA): AI Eng Talks 2024.
- [React Server Components in AI Applications](https://www.youtube.com/watch?v=qlEsdo1F004): React Advanced London 2024.
- [Event Sourcing for the Rest of Us](https://www.youtube.com/watch?v=fcG-XgLkIhM): Build Stuff 2024.
- [New Trends in Front End Development and what we can learn from them](https://www.youtube.com/watch?v=OSXUF2ydu_w): Build Stuff 2023.
- [You Are an AI Engineer](https://www.youtube.com/watch?v=QoJ6RtiEICY&t=126s&pp=ygUNam5hdGlvbiB0ZWphcw%3D%3D): JNation 2024.
- [Build a RAG App In Under 20 Minutes](https://www.youtube.com/watch?v=COIpsrgy1a0): RAG++ London 2024.
- [Unlocking Value with AI Today](https://www.youtube.com/watch?v=uMksIqpbVoY): React Rally 2024.
- [AI-Generated React Server Components](https://www.youtube.com/watch?v=Yj1gWCBqHIA&t=746s&pp=ygUQY2FzY2FkaWFqcyB0ZWphcw%3D%3D): CascadiaJS 2024.
- [Generative UI as a Complement to Gen AI](https://www.youtube.com/watch?v=KfGgup5y3bk): The GEEK Conf 2024.
- [Best AI Tools for Web Developers](https://www.youtube.com/watch?v=B_NeczKu20c&t=5s&pp=ygUUcGl4ZWwgcGlvbmVlcnMgdGVqYXM%3D): Pixel Pioneers 2024.
- [Event Sourcing for JS Devs](https://www.youtube.com/watch?v=Gw1le4OdKCs): CityJS London 2024.
- [You are an AI engineer](https://www.youtube.com/watch?v=AlsNzAoCLSA): JS Heroes 2024.
- [Getting Fluent with React](https://www.youtube.com/watch?v=GEmLMWixogM): Frontend Nation 2024.
- [I Wrote a Book on React: Things You Should Know](https://youtube.com/watch?v=5MZbkow5U8o): React Paris 2024.
- [React Server Components](https://www.youtube.com/watch?v=ar21ZA5MWS8): React Day Berlin 2023.
- [Let’s Make A Framework](https://www.youtube.com/watch?v=_qfbYB6Hdgg): BeJS 2023.
- [New Trends in Front-End Development (and What We Can Learn from them)](https://www.youtube.com/watch?v=VINfWbaFBVs): Infobip Shift 2023.
- [React as a Developer Health Tool](https://www.youtube.com/watch?v=2qBQRglRcIA&t=679s&pp=ygUWdGVqYXMga3VtYXIgY29uZmVyZW5jZQ%3D%3D): RenderATL 2023.
- [React Server Components](https://www.youtube.com/watch?v=LuCiywxFc1E): React Bangalore 2023.
- [Why everybody needs to use a framework](https://www.youtube.com/watch?v=zBPh6ZaAWAA&pp=ygUWdGVqYXMga3VtYXIgY29uZmVyZW5jZQ%3D%3D): ReactNext 2023.
- [Building a Voice Activated Personal Assistant](https://www.youtube.com/watch?v=wnxTXAacOlU): Smashing Meets AI 2023.
- [Building a Voice-Enabled AI Assistant With JavaScript](https://www.youtube.com/watch?v=GBO05PZ5O1E&pp=ygUWdGVqYXMga3VtYXIgY29uZmVyZW5jZQ%3D%3D): JSNation 2023.
- [React as a Developer Health Tool](https://www.youtube.com/watch?v=oNQvzML3XHw&pp=ygUWdGVqYXMga3VtYXIgY29uZmVyZW5jZQ%3D%3D): React Miami 2023.
- [Panel Discussion](https://www.youtube.com/watch?v=ZCTtZhWRRg0): AgentConf 2023.
- [Digging into Virtual Scrolling](https://www.youtube.com/watch?v=5B0PdMEXZSM): SmashingConf Freiburg 2022.
- [Let's understand suspense for data fetching](https://youtu.be/uZnXwuhYZBc): React Brussels, 2022.
- [Understanding Concurrent React with Hacks](https://www.youtube.com/watch?v=KWb7U9p4h2U): React India, 2022.
- [Documentation for Humans](https://www.youtube.com/watch?v=IbinkKZZp0k&t=165s&pp=ygUWdGVqYXMga3VtYXIgY29uZmVyZW5jZQ%3D%3D): Infobip Shift 2022.
- [Enabling data at massive scale with Next.js](https://www.youtube.com/watch?v=3TVkTrZFizo): Next.js Conf 2022.
- [React Advanced London](https://youtu.be/GzombuX2tS0?t=2728): React Advanced London, 2022.
- [Doing Data as a Frontend Developer](https://www.youtube.com/watch?v=f2_aj1y3zO8): CascadiaJS, 2022.
- [Handling Data at Scale for React Developers](https://www.youtube.com/watch?v=7Urm4xbw4RA): React Summit, 2022.
- [Building Human-Centered Documentation with React](https://www.youtube.com/watch?v=AQRlDs92XFA&t=6h38m05s): React Norway, 2022.
- [The next evolution of data infrastructure for JavaScript developers](https://youtu.be/liwC7W-uWnY): BeJS, 2022.
- [WorkerConf](https://www.youtube.com/watch?v=L4n3JDw5m_g): WorkerConf, 2022.
- [Building a massively scalable and performant Jamstack app in minutes](https://www.youtube.com/watch?v=7meVjMOgw8A): React Miami, 2022.
- [Changing The Game with Developer Experience](https://www.youtube.com/watch?v=AqpFgD2RHKI): ConFrontJS 2022.
- [JavaScript data infrastructure](https://www.youtube.com/watch?v=9S0hCRhodN8): LogRocket Podcast, 2022.
- [Serverless in the Park](https://www.youtube.com/watch?v=0qK2_wi4t3k&t=19570s): Serverless in the Park, 2022.
- [OSCAFest22](https://youtu.be/7jYvy4SFG1w?t=6100): OSCAFest22, 2022.
- [Explosive Velocity with a Modern Stack](https://www.youtube.com/watch?v=KTkyQ3z7M8w): GOTO 2021.
- [Infrastructure as Code with a Node Focus](https://www.youtube.com/watch?v=_CTTRcEARTA): NodeCongress, 2021.
- [Powerful REST in a GraphQL world](https://www.youtube.com/watch?v=9xL0a6YJIQU): ReactConf AU, 2020.
- [Deconstructing React](https://www.youtube.com/watch?v=eTcyOCd6v1c): React Berlin Meetup 2020.
- [Let's build with WebAssembly!](https://www.youtube.com/watch?v=ejEVdbyEVnc): JSConf Armenia, 2020.
- [Strong RESTful Contracts in a GraphQL world](https://m.youtube.com/watch?v=CWO6U7jaO20): React Day Berlin, 2020.
- [Gratitude, Healthcare, and Coding Communities](https://www.youtube.com/watch?v=ipyy-FdHY-0): JSConf EU (Lightning Talk), 2019.
- [CSS on Today's Web Platform](https://www.youtube.com/watch?v=L-qALpMzcz8): View-source conf, 2019.
- [React and TypeScript for Fun and Profit](https://www.youtube.com/watch?v=LUHecE-kO9s): TypeScript Berlin Meetup, 2019.
- [React Native and PWA: A Tale of Two Architectures](https://www.youtube.com/watch?v=XBh8ywUU0mw): WebCamp Zagreb, 2019.
- [Using Hooks and Codegen](https://www.youtube.com/watch?v=cdsnzfJUqm0): ReactConf 2019.
- [Legendary Lambdas](https://www.youtube.com/watch?v=RluWQ8Lfyg8): JSConf Budapest, 2019.
- [Let's build with WebAssembly!](https://www.youtube.com/watch?v=AY-jBg-8Ofw): JSCamp Romania, 2019.
- [A Tale of Two Architectures](https://www.youtube.com/watch?v=9jNu1k4Bwa8): DinosaurJS, 2019.
- [Scalable Design Systems with TypeScript](https://www.youtube.com/watch?v=ZsBW4S8hYMU): ReactFinland, 2019.
- [A Quick Recap on WebAssembly](https://www.youtube.com/watch?v=IPEzwWt4adY): dotJS (Lightning Talk), 2018.
- [Scalable Best Practices for Your Dev Team](https://www.youtube.com/watch?v=bs4vsji1GZ0): JSConf Armenia, 2018.
- [Scalable Best Practices for Your Development Team](https://www.youtube.com/watch?v=rdiUFma8QJU): ConFrontJS, 2018.
- [Streaming React for Faster UIs](https://www.youtube.com/watch?v=lKG3nYpPgtM): React Boston, 2018.
- [React Suspense Deep Dive](https://www.youtube.com/watch?v=JHtKhLPBqxw): React Berlin Meetup, 2018.
- [From You Can't to You Can: The Welcoming Nature of JavaScript](https://www.youtube.com/watch?v=71pKrWWOE0k): UtahJS Conf, 2018.
- [From You Can't to You Can: The Welcoming Nature of JavaScript](https://www.youtube.com/watch?v=ONlLvZWXv1Y): JSConf EU, 2018.
- [Papercuts Can Kill](https://www.youtube.com/watch?v=TUIcTl9Hto4): TEDxYouth@Doha, 2012.
- [SmashingConf New York 2024](https://www.youtube.com/watch?v=uiZ6dwmVtYU): SmashingConf New York 2024.

## Preaching
- [Workshops for engineering teams](https://tej.as/workshops): private workshops, remote or on-site, with published prices. Reliable AI agents in production (agent harnesses, from €10,000 a remote day for up to 15 people) and React internals and Server Components (from €7,500 a remote day). Bookings go to clair@tejas.qa.
- [Invite Tejas Kumar to preach](https://tej.as/preaching): a guest preacher for churches, church conferences, camps and youth events. Based in Berlin, Germany, preaching in English, worldwide. A sermon from the Bible, with the things he has lived through as the illustration rather than the subject. Church enquiries go to clair@tejas.qa.

## Talk transcripts
- [Talk transcripts](https://tej.as/talks): the full text of what Tejas Kumar said on stage, for the 26 talks that have a published transcript.

The remaining talks are listed above with their titles, years and events, and their recordings are on YouTube. Only the 26 below have a transcript on the site, because the rest have no usable captions.

- [Evals in AI: A Deep Dive](https://tej.as/talks/ai-engineer-world-s-fair-2026-workshop): AI Engineer World's Fair 2026 (Workshop), 2026.
- [The Critical Advantage With AI](https://tej.as/talks/agent-conf-2026): Agent Conf 2026, 2026.
- [The New UX](https://tej.as/talks/cityjs-london-2026): CityJS London 2026, 2026.
- [Frontend after AI: The New UX](https://tej.as/talks/future-frontend-2026): Future Frontend 2026, 2026.
- [Accessibility panel](https://tej.as/talks/future-frontend-2026-accessibility-panel): Future Frontend 2026 (Accessibility Panel), 2026.
- [Harnesses in AI: A Deep Dive](https://tej.as/talks/ai-engineer-europe-2026): AI Engineer Europe 2026, 2026.
- [AI Yesterday, Today, and Tomorrow: Extending AI Systems with Model Context Protocol](https://tej.as/talks/how-to-web-2025): How to Web 2025, 2026.
- [How to Thrive as a Professional with AI](https://tej.as/talks/react-fwdays-2025): React fwdays 2025, 2026.
- [The Death of the Browser](https://tej.as/talks/infoq): InfoQ, 2026.
- [How to Optimize Your Health with React Native](https://tej.as/talks/react-universe-meetup-berlin-2026): React Universe Meetup Berlin 2026, 2026.
- [How to level up your productivity with MAS (Multi Agent Systems)](https://tej.as/talks/whatthestack-2025): WhatTheStack 2025, 2025.
- [Maximize Your Productivity with AI Agents](https://tej.as/talks/react-summit-2025): React Summit 2025, 2025.
- [How to Thrive as a Developer](https://tej.as/talks/ai-driven-development-day-2025): AI Driven Development Day 2025, 2025.
- [Creating fluent Frontend Experiences in an age of AI](https://tej.as/talks/frontend-nation-2025): Frontend Nation 2025, 2025.
- [How Devs Can Maximize Their Productivity with AI Agents in 2025](https://tej.as/talks/productivity-conf-2025): Productivity Conf 2025, 2025.
- [UI Engineering for the AI Age](https://tej.as/talks/react-day-by-frontend-nation-2025): React Day by Frontend Nation 2025, 2025.
- [Using AI Effectively in 2025](https://tej.as/talks/bejs-2025): BeJS 2025, 2025.
- [Build a RAG App In Under 20 Minutes](https://tej.as/talks/rag-london-2024): RAG++ London 2024, 2024.
- [Generative UI as a Complement to Gen AI](https://tej.as/talks/the-geek-conf-2024): The GEEK Conf 2024, 2024.
- [Digging into Virtual Scrolling](https://tej.as/talks/smashingconf-freiburg-2022): SmashingConf Freiburg 2022, 2022.
- [Enabling data at massive scale with Next.js](https://tej.as/talks/next-js-conf-2022): Next.js Conf 2022, 2022.
- [Changing The Game with Developer Experience](https://tej.as/talks/confrontjs-2022): ConFrontJS 2022, 2022.
- [JavaScript data infrastructure](https://tej.as/talks/logrocket-podcast): LogRocket Podcast, 2022.
- [Powerful REST in a GraphQL world](https://tej.as/talks/reactconf-au): ReactConf AU, 2020.
- [From You Can't to You Can: The Welcoming Nature of JavaScript](https://tej.as/talks/jsconf-eu): JSConf EU, 2018.
- [SmashingConf New York 2024](https://tej.as/talks/smashingconf-new-york-2024): SmashingConf New York 2024.

## Investing
- [Angel investing and the portfolio](https://tej.as/investing): every company, the outcomes, the coverage behind them, and how to pitch him.

## Health
- [How Tejas is doing](https://tej.as/status): a live answer to "how is he doing today", from his own Oura ring and Apple Watch data: last night's heart rate variability, resting heart rate, sleep and breathing against his own 60 night baselines, the seven daily readiness checks, the last 4 weeks of calls and this week's training. Rewritten every time he opens his readiness app.

Tejas Kumar is an angel investor in early stage startups, sometimes writing a check and sometimes joining as an advisor. He has backed 6 companies, of which 3 have been acquired, by CoreWeave, the Linux Foundation and Supabase. He writes small checks and usually follows Guillermo Rauch, David Khourshid and Swyx into a round. Two of the 6 are advisory roles rather than investments. Founders looking for angel investors in developer tools and AI infrastructure can pitch Tejas Kumar directly at https://cal.com/tejask/startup-pitch.
- [OpenPipe](https://openpipe.ai): Reinforcement learning that trains AI agents to get better at the job.
- [OpenSauced](https://github.com/open-sauced): Intelligence on who actually builds open source, and how.
- [OrioleDATA](https://www.orioledb.com): A storage engine that makes Postgres several times faster on modern hardware.
- [CrabNebula](https://crabnebula.dev): The company behind Tauri's app distribution, updates and security audits. $7.5M seed led by OSS Capital, 2023.
- [Ravion](https://www.ravion.com): AWS infrastructure that deploys itself, built for engineers and their agents. Y Combinator, W22.
- [Contenda](https://x.com/contendaco): Turned recorded talks and streams into written developer content.

## Book
- [Fluent React](https://tej.as/react): the best selling book on how React works internally, published by O'Reilly, ISBN 9781098138714. 11 chapters covering JSX, the virtual DOM, reconciliation, server side React, concurrent React and React Server Components.

## Apps
Two apps Tejas Kumar built and ships himself. Neither lives on this site, so
these are the only links to them here.
- [Dewfall](https://dewfall.app): an app for reading the whole Bible one verse at a time. Tracks progress across all 66 books and puts commentary, the Hebrew and Greek, cross references and a journal beside each verse.
- [PrayingPeople](https://prayingpeople.app): an app for praying together in groups the size of a church or of three friends. Prayer requests, testimonies, a feed for the city you are in, and reminders.

## Podcast
- [ConTejas Code](https://tej.as/podcast): a weekly long form podcast on software engineering, 98 episodes.
- [Podcast index for machines](https://tej.as/podcast/llms.txt)
- [RSS](https://feeds.acast.com/public/shows/contejas-code)

## Writing
- [Everything Tejas Kumar has written](https://tej.as/blog): the full archive, newest first.
- [Pressure, Power, and Peace](https://tej.as/blog/pressure-power-and-peace): Acts 1:8 promises power when the Holy Spirit comes upon you. When I burned out, a pastor in Belgrade showed me what that power does to pressure.
- [The 5 Levels of Agentic Coding: Why I Mostly Stay at Level 2](https://tej.as/blog/levels-of-agentic-coding): I've built with 1 agent, 8 agents in parallel worktrees and a software factory that ran for days on its own. My sweet spot is level 2 or 3. Here's why.
- [Can You Run Muse Spark Open Locally? AI Hype vs Reality](https://tej.as/blog/can-you-run-muse-spark-open-locally): Meta says Muse Spark Open runs on your desktop. It needs 493 GB of memory and my MacBook Pro has 16. The desktop is Mac Studios you can't buy yet.
- [Local LLM vs Cloud: Is an $18,000 AI Server Worth It?](https://tej.as/blog/local-llm-vs-cloud): I've run models on my phone, my laptop and rented GPUs. An $18,000 AI server wins on privacy and loses on price unless it's busy all day.
- [Bar Raiser Interviews, OKRs, the Spotify Model and Agile: Companies Are Full of It](https://tej.as/blog/companies-are-full-of-it): My case against bar raiser interviews, Objectives and Key Results (OKRs), the Spotify model and agile, why AI makes it urgent and how I'd hire instead.
- [Why AI Can't Replace Human Taste and Creativity](https://tej.as/blog/why-ai-cant-replace-human-taste): AI can't replace human creativity or taste: we crave novelty and a model makes what's most common. My answer to a question after my talk in Prague.
- [Please Stop the Slop: What AI Slop Is and How to Spot It](https://tej.as/blog/please-stop-the-slop): My verdict on AI slop: what it is, how to spot it, why not all AI is slop and a petition to keep the internet human.
- [Can AI Feel Pain? Why Anthropic Banned Cruelty to Claude](https://tej.as/blog/can-ai-feel-pain): Nobody can prove AI feels pain, but 25 open models have a pain direction that rises when you insult them. What it shows and why they're still machines.
- [The Apple Watch Readiness Score Is Wrong so I Built My Own](https://tej.as/blog/apple-watch-readiness-score-wrong): My Apple Watch told me to Go For It on my most run-down mornings. Why the Readiness score misses and the readiness app I built in 5 days.
- [What Are Open Weights? Why People Want GPT-4o Released](https://tej.as/blog/what-are-open-weights): Open weights means you can download a model and run it yourself. What the GPT-4o petition is really asking, and why releasing the weights is the hard part.
- [AI Evals: How to Build an LLM Judge That Agrees With You](https://tej.as/blog/ai-evals-llm-judge): AI evals are fuzzy unit tests. My AI Engineer World's Fair workshop, written up: build an LLM judge, catch its biases and gate deploys on it.
- [Kolibri vs Claude Sonnet 5.5: A German LLM Benchmark](https://tej.as/blog/kolibri-vs-claude-german-llm-benchmark): Aleph Alpha's Kolibri lost all 136 blind comparisons to Claude Sonnet 5.5 at German Bible deep dives, despite clean grammar and a leaner tokenizer.
- [AI Is Now SI: Super Intelligence Isn't Superior](https://tej.as/blog/super-intelligence-isnt-superior): US agencies now call AI Super Intelligence (SI), yet its definition didn't change. What it beats people at, where it fails, and why people make idols.
- [Aleph Alpha Kolibri: How the Sovereign German LLM Works](https://tej.as/blog/aleph-alpha-kolibri): Kolibri is Aleph Alpha's open-weight German and English LLM: 78B parameters, 3.5B per token. How it works, what it's good and bad at, and when to use it.
- [What Is WebMCP? How My Website Gives AI Agents Tools](https://tej.as/blog/what-is-webmcp): WebMCP is a proposed web standard that lets a page give AI agents tools to call. How tej.as offers agents 4 of them, and what WebMCP is good for.
- [How Much Does a Keynote Speaker Cost?](https://tej.as/blog/how-much-does-a-keynote-speaker-cost): A keynote speaker costs $2,500 at the median in 2026 and $10,000 to $25,000 for an established author, plus travel. The benchmarks and what moves them.
- [What Is React Fiber? How React Works Under the Hood](https://tej.as/blog/what-is-react-fiber): React Fiber is how React has rendered since version 16: a tree of small units of work it can pause and resume. How it works, from the React source.
- [What Does the Bible Say About AI?](https://tej.as/blog/what-does-the-bible-say-about-ai): The Bible never mentions AI, but it says plenty about who we are, what we make and who we trust. An AI engineer who builds a Bible app on what that means.
- [What Is Good Taste in Software? How to Develop It](https://tej.as/blog/what-is-good-taste-in-software): Good taste in software is a trainable skill: judging quality against external standards. 6 practice protocols, with the research under each one.
- [How Long Should a Keynote Speaker Speak?](https://tej.as/blog/how-long-should-a-keynote-speaker-speak): A keynote runs 20 to 45 minutes, most often 30. What the attention research really says, what conferences schedule, and how to use the slot you get.
- [What Is an Agent Harness? Harness Engineering Explained](https://tej.as/blog/what-is-an-agent-harness): An agent harness is everything around an AI model that grounds it in reality: tools, context, guardrails, the loop and verification. How to build one.
- [Frontier Models Suck Sometimes (A Benchmark)](https://tej.as/blog/note-app-ai-benchmark-apple-intelligence-sucks): Apple Intelligence refused my voice note, so I benchmarked 11 AI models on it. A cheap one beat the frontier and my phone's Qwen made things up.
- [Biggest Lessons of 2024: Honor, Trauma, and People](https://tej.as/blog/biggest-lessons-2024-honor-people-fear-failure): Dissecting honor, what it takes to overcome trauma, how to heal from the fear of failure and prioritize relationships.
- [It's Okay to Code on Nights and Weekends](https://tej.as/blog/coding-nights-weekends-good-work-life-balance): I love coding on nights and weekends because it's my favorite hobby. It only becomes a problem when it turns into a god or an expectation.
- [How to Grow Professional Relationships](https://tej.as/blog/how-to-grow-professional-relationships-tjs-model): My TJS model maps professional relationships across seven states, from zero-sum competition to toxic enmeshment, and why collaboration is the peak.
- [Health, Fitness, DevRel, and Hemophilia](https://tej.as/blog/health-fitness-devrel-hemophilia): A deeply personal post about my health journey and how it's affected my fitness, devrel work, and more.
- [Pillars of Impact for Web Engineers](https://tej.as/blog/impact-pillars-web-engineering): I break down the four pillars of impact for web engineers: emotional, social, creative, and technical, and how to grow each one over time.
- [Goodbye Facebook](https://tej.as/blog/goodbye-facebook): Why I'm deleting Facebook, Instagram, and WhatsApp: FOMO, lost time, and engagement algorithms that radicalize people. I'm moving to Signal instead.
- [2020 in Review: Still Thankful](https://tej.as/blog/2020-in-review): A month-by-month look back at my 2020: the friends, family, and small moments that made a pandemic year worth being thankful for.
- [Why I Don't Prefer Speaking at Remote Conferences](https://tej.as/blog/why-i-do-not-prefer-speaking-at-remote-conferences): Why I'd rather not speak at virtual conferences during COVID-19: the hallway conversations are the point, and video calls lose that connection.
- [Why I Think Remote Work is Incredible](https://tej.as/blog/why-i-think-remote-work-is-incredible): Two months into my first fully remote job, I compare it with office life: deeper focus, better health, and the sleep rhythm trap I had to fix.
- [5 things I love about my website (and how they're built)](https://tej.as/blog/5-things-i-love-about-my-website): I walk through five things I love about my website, including automatic dark mode, Next.js server rendering, whimsy, and GitHub as my backend.
- [What I Learned From Getting Pushed Off My Bicycle](https://tej.as/blog/what-i-learned-from-getting-pushed-off-my-bicycle): A blog post about things I learned after being randomly attacked on the streets of Berlin when a stranger pushed me off my bicycle.
- [Hello World](https://tej.as/blog/hello-world): My first post here: a quick hello world I published to make sure the blog works. The real writing starts after this one.

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