Hello there! My name is
Darius Cepulis
I make great web experiences.
About me

I make sure devs have a great experience with Mux. I think the web is pretty neat!
I'm a Senior Developer Experience Engineer at Mux. Team lead, actually!
In DevEx, we're doing anything we can to design and develop a better experience for devs. (Go figure!) Handy components, a delightful marketing site, a better dashboard, useful docs, and some content on the side.
Fun fact about me, I actually like writing CSS. Weird, huh?
I went to school for Computer Engineering, thinking I'd end up writing assembly or something for some low-level hardware. After that scared the bejeebies out of me, I ran away as fast as I could, as far as I could, to the web, where I found a home.
When my dad asked me about why I ended up in web development, I told him that it's a lot like the deck that he built in his back yard. It's building a space that serves a practical use. But it's also more than that. It's also thinking about how the user will move through that space, from beginning to destination. Also how that space will fulfill its purpose without getting in the way. How the user will enjoy that space. The details that will delight them. How that space will work for all the different kinds of people who will interact with it.
Lately, I've been realizing that the design skills I learned making static web pages work across all of developer experience. From components, to a marketing site, a dashboard, docs, even some contentโฆ It's all just ways to lower the bar for users trying to get stuff done. That's the kind of stuff I get to design and develop as a Senior Developer Experience Engineer at Mux. And as a team lead, I'm helping other folks do that, too.
Some things I've been up to
What the iPhone Duo means for web development (and Video.js)
A weekend with the iPhone Duo simulator, folding-phone web APIs, and a Netflix-style folded player built with Video.js.
๐ ๐CascadiaJS 2026: Choosing the wrong abstraction (and what it cost us)
API design is hard. Composition might be the answer?
๐ฃ๏ธ ๐Video.js 10
Helping build the next generation of video players. As an IC, I spend most of my time thinking about docs and agentic workflows. As team lead, process and people.
โ๏ธEven devtools need great dashboards
Weโve made some big changes to the Mux dashboard, and learned some big lessons about developer experience along the way
๐ ๐Mux home page
Telling an interactive story of a developer tool, from simple embeds to deep workflows
โ๏ธTailwind is the worst form of CSS, except for all the others
Opinionated tools are good for you and your teamโฆ even if you disagree with the opinion.
๐ ๐Dainorฤlis: your Lithuanian songbook
I grew up singing Lithuanian songs by the campfire. So it meant a lot to me to take over the Dainorฤlis app. I rewrote it in React Native, updated its design, added hundreds of new songs, and built ways for people to learn through chords, sheet music, and recordings.
โ๏ธWe want your LLM to read our docs
Is it hype-driven development? Or is there actually something to the trend of adding llms.txt to our websites?
๐ ๐Mux Player iframe and playback page
A little hack week project that I brought over the line... with a few useful easter eggs!
โ๏ธ ๐Magnification loupe
I love this little detail, that took me three days of CSS to get right...
โ๏ธDemuxed 2024 website
An incredible design that just begged to have a fully-interactive Mac OS 9 style window manager developed for it. So that's what I did!
โ๏ธMux vs. Cloudflare Stream
A great example of the kind of everyday work that doesn't normally show up on my portfolio
โ๏ธAI chatbots are banned from our docsโฆ for now
Why we decided not to use an AI chatbot in our docs, and what that says about the state of LLMs
๐ ๐Learn With Jason - Put videos behind auth
Jason Lengstorf and I talk about the levels of stream security you can use with Mux
๐ฅ ๐React 19 lets you write impossible components
An adaptation of my React Miami talk
๐ ๐React Miami 2024: Living with Server Components after the honeymoon
I gave a workshop/talk at React Miami 2024! The honeymoon, the reality, and the surprisingly optimistic future of React Server Components.
๐ฃ๏ธWhy are video players so big?
A simple question with a fascinating answer
๐ ๐next-video.dev
Quickly building a slick marketing site for our new library
โ๏ธNext.js Conf 2023: How to migrate 50,000 lines of code to RSC
I spoke at Next.js Conf! The talk was an adaptation of my React Server Components blog post.
๐ฃ๏ธ ๐Can React Server Actions finally fix forms?
An early look at React Server Actions
๐ ๐Everything I wish I knew before moving 50,000 lines of code to React Server Components
Thoughts, comments, and concerns about being an RSC early adopter. My blog post with a bit of a viral moment!
๐Mux marketing site rebrand
Rebuilding the Mux marketing site from the ground up with a new brand, new component library, and new React Server Components. I'm so proud of our hard work. I'm still trying to catch up on sleep.
โ๏ธMux Docs v3
With a growing product, we needed to update our docs with a new information architecture. Next thing we knew, we were also updating our codebase to Server Components... dangerously early!
โ๏ธThe building blocks of great docs
Why we built Docs v3, and about our migration to Tailwind and React Server Components.
๐ ๐@mux/blurhash
Using woltapp/blurhash to make nice placeholders for Mux videos.
โ๏ธHow we made Mux Playerโs loading feel great
Writing about the creation of @mux/blurhash
๐ ๐Mux Player page
Scrollytelling with Mux Player
โ๏ธThe Mux Informational site
Worked with our top-notch designers on an alarmingly short notice to really go all-in on this incredible vibe.
โ๏ธReal-Time Video page
Launching a whole new product at Mux with with some really slick animations
โ๏ธOur photo gallery
A place for me to put our slideshows so I wouldn't have to bore people in person!
โ๏ธThis website!
A place to talk about myself and play with new web tech
โ๏ธFormula fun!
Moneyballing the heck out of a friendly F1 wager
โ๏ธServerless Weasley clock
Using the JAMStack to achieve my hardware dreams
โ๏ธMicrosensor Labs site
Designing and building a lightweight marketing/blog/job listing site
โ๏ธSanibit UI
Gamifying hand hygiene to improve hand hygiene, fight infections, and save lives
โ๏ธSanibit server
Crunching millions of data points to improve hand hygiene, fight infections, and save lives
โ๏ธMidwest Microbio site
A minimal marketing website designed and built for a buddy's budding beer business
โ๏ธCreating socio-technical patches for information foraging
Thesis, presented at VL/HCC 2018
๐ฃ๏ธSensor analytics platform
How I (accidentally) got into web development
โ๏ธMoreโฆ
See more, including my graveyard of half-finished projects, on GitHub.
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