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Daniel Hoelzgen

@dhoelzgen.dev
997 followers 645 following 76 posts

#ElixirLang and #Ruby Lead Developer at 9elements, an agency for outstanding digital products. Focused on Artificial Intelligence, Logic, and Data Visualization.

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Daniel Hoelzgen @dhoelzgen.dev · 26/08/2026
Joint meetup with the Elixir Cologne group, Phoenix flavored talk about accessibility, and barbecue at the rooftop. Excited about a very special #elixir meetup!
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Daniel Hoelzgen @dhoelzgen.dev · 02/07/2026
After not being able to attend last year, I'm really excited to be at Ash summit in 2026. If you are at Goatmire, think about staying a day longer!
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Daniel Hoelzgen @dhoelzgen.dev · 21/05/2026
Thank you, this means a lot to us. Elixir has been steadily becoming a bigger part of what we do at 9elements, and that growth has been shaped by the openness and warmth of the BEAM community. We are glad we can support this awesome community by sponsoring Code BEAM Europe!
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Daniel Hoelzgen @dhoelzgen.dev · 22/04/2026
Most of the @9elements.com elements team for @elixirconf.bsky.social EU 2026 arrived in Málaga. Looking forward to an awesome conference and to catching up with everyone here. Come say hi whenever you see us around. #elixirlang
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Daniel Hoelzgen @dhoelzgen.dev · 06/03/2026
I am proud that @9elements.com is sponsoring ElixirConf EU this year! For us, ElixirConf is one of the most important gatherings in the Elixir ecosystem. The talks are inspiring, and the community is genuinely one of the friendliest in tech. Can't wait to be part of it. #ElixirConf #ElixirLang
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Reposted by Daniel Hoelzgen
Zach Daniel @zachdaniel.dev · 26/02/2026
usage_rules now supports copying skills from your packages in addition constructing skills from the usage rules files 😎 Package authors can now provide entire skills for your project, and when you update your dep you can get the new version of the skill! #ElixirLang
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Daniel Hoelzgen @dhoelzgen.dev · 26/02/2026
Our team built the app backend for a major German sports club, and it was one of the most exciting projects to come out of @9elements.com. Can't wait to listen to @nickidee.bsky.social's talk to get some insight on how they handled scalability and performance.
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Daniel Hoelzgen @dhoelzgen.dev · 22/01/2026
Booked my ticket for Elixir Conf 2026 in Málaga, looking forward to a few great days with the community. Happy to have four coworkers joining me this year.
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Daniel Hoelzgen @dhoelzgen.dev · 03/12/2025
Quite impressed that we have 40 registered attendees, looking forward to the meetup tomorrow!
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Daniel Hoelzgen @dhoelzgen.dev · 11/11/2025
We just announced our next Elixir Ruhr meetup! Looking forward to Christoph's talk, and to plenty of great conversations with the local community
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Daniel Hoelzgen @dhoelzgen.dev · 26/09/2025
I am pleased to share that @9elements.com is sponsoring @codebeam.bsky.social Europe 2025! As we continue strengthening our focus on Elixir, Phoenix, and Ash, it feels great to also deepen our role in this wonderful community. Looking forward to meeting many of you in Berlin!
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Elixir Ruhr @elixir-ruhr.dev · 26/09/2025
Nearly thirty people joined our first meetup yesterday and we're so happy you came. Thank you for the great conversations and for helping us grow the local #elixirlang community!
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Daniel Hoelzgen @dhoelzgen.dev · 26/09/2025
Grateful that our first @elixir-ruhr.dev meetup brought together so many people - Our local community feels stronger than ever! Had a lot of fun talking about @ash-hq.org. A big thank you to @discord.com for saving the day when streaming didn’t go as planned. Join us here: discord.gg/TRqQcxRMjq
discord.gg
Join the Elixir Ruhr Discord Server!
lixir Ruhr is a welcoming meetup for everyone excited about Elixir, Erlang, and the BEAM community. All experience levels are welcome! | 22 members
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Zach Daniel @zachdaniel.dev · 11/09/2025
The video for my talk at Scenic City Summit is up! Building on Bedrock: Elixir's Fundamental Design Advantage youtu.be/pir_vDhnVys?... #ElixirLang
youtu.be
Building on Bedrock: Elixir's Fundamental Design Advantage - Zach Daniel
YouTube video by ChaTech Council
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Daniel Hoelzgen @dhoelzgen.dev · 10/09/2025
Working on a small example app for my upcoming @elixir-ruhr.dev talk about @ash-hq.org. Really impressed how easily Ash AI integrates complex LangChain tool calls with just a few lines of code!
A screenshot of a chat-bot web application, responding with a list of events to the user query to list Elixir / Ash related events coming up this month.
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Software Mansion Elixir @swmansionelixir.bsky.social · 05/09/2025
The question isn’t if you’ll join, but where. 💎 Find your GEM: globalelixirmeetups.com
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Daniel Hoelzgen @dhoelzgen.dev · 03/09/2025
Really looking forward to our first Elixir Ruhr Meetup! I'll be giving an introduction to @ash-hq.org & Ash AI. Been having lots of fun with it lately and can't wait to share. Excited for good conversations and a great evening with the community. #elixirlang #myelixirstatus
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Zach Daniel @zachdaniel.dev · 28/08/2025
Expert LS is out yall. #ElixirLang github.com/elixir-lang/...
github.com
GitHub - elixir-lang/expert: Official Elixir Language Server Protocol implementation
Official Elixir Language Server Protocol implementation - elixir-lang/expert
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Daniel Hoelzgen @dhoelzgen.dev · 20/08/2025
Looks like I found something new to read for the next couple of days: Advanced Functional Programming with #ElixirLang,just released as beta on @pragprog.com pragprog.com/titles/jkeli...
pragprog.com
Advanced Functional Programming with Elixir
Use advanced functional programming principles, practical domain-driven design techniques, and production-ready Elixir code to build scalable, complex systems from simple, reusable components.
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Daniel Hoelzgen @dhoelzgen.dev · 18/08/2025
Really happy to finally move forward with rebuilding the local #elixirlang meetup in the Ruhr area. If you’d like to be part of it, join our Discord or just reach out to me here.
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Zach Daniel @zachdaniel.dev · 29/07/2025
This is a really cool project! github.com/bradleygolde... Think of it like a Quickstart for working with claude code and Elixir projects, that leans on all the conventions we've been working on like tidewave & usage rules. #ElixirLang
github.com
GitHub - bradleygolden/claude
Contribute to bradleygolden/claude development by creating an account on GitHub.
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Daniel Hoelzgen @dhoelzgen.dev · 30/06/2025
We are looking for an #elixirlang / #rubylang lead developer in Bochum / the Ruhr area. If you love building great software instead of managing bullshit tickets, know how to work with clients and how to make sure your team grows, let's chat!
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Daniel Hoelzgen @dhoelzgen.dev · 27/06/2025
As AI redefines software development, this post by @ichimnetz.com stands out; tracing how automation shifts value from craft to concept, from 19th-century painting to today’s programming. Appreciate he draws thoughtful parallels without pretending to predict where it all leads.
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Daniel Hoelzgen @dhoelzgen.dev · 17/05/2025
#ElixirConf 2025 was absolutely wonderful. First one since 2017, and the community is still just as great, lovely, and open. Tons of inspiring talks and conversations, can’t wait to try Ash AI! See you at the next one, hopefully not in another 7 years.
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Daniel Hoelzgen @dhoelzgen.dev · 13/05/2025
So excited for the upcoming @elixirconf.bsky.social in Krakow - Can’t wait for all the amazing talks and to meet more awesome folks in the #elixirlang community!
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Daniel Hoelzgen @dhoelzgen.dev · 17/04/2025
If you need your LLM to follow instructions better, try GPT-4.1. I’m building a chatbot with more complex behavior and struggled to get 4o to follow instructions properly. Switching to 4.1 fixed it, even without gimmicky styles to signal what's important.
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Daniel Hoelzgen @dhoelzgen.dev · 28/02/2025
This morning, I talked with my daughter about weekdays - specifically, what day it will be after a given number of days. I explained that adding multiples of seven doesn’t change the weekday, only the remainder matters. Not the easiest concept for a four-year-old.
A digital interface displays a ‘Weekdays’ calendar with a colorful and playful design. The top section includes a row of buttons representing days of the week, each paired with an emoji (e.g., a moon for Monday, fire for Tuesday, water drop for Wednesday). Below, a number input with plus and minus buttons allows for selecting a numerical value, currently set to 15. The lower section presents a calendar-like grid with labeled weekdays and corresponding numbers. Some days are highlighted in different colors, such as Friday (yellow) and Saturday (pink). An arrow and emojis (a sprout and a rainbow) suggest a transformation or mapping concept. The overall aesthetic features soft purple tones with bold, rounded typography.
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Daniel Hoelzgen @dhoelzgen.dev · 20/02/2025
Yesterday, I released a tiny MCP server that allows Cursor Editor to get up-to-date version information for external Hex dependencies. Someone suggested doing a version for #RubyOnRails, so I built a more generic version that supports Ruby Gems, Hex, PyPI, and NPM. dep-mcp.9elements.com
dep-mcp.9elements.com
Package Version MCP Server - For AI Tools
Help AI tools like Cursor to automatically use the correct package versions when adding dependencies to your projects. Supports Hex, RubyGems, and NPM packages.
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Daniel Hoelzgen @dhoelzgen.dev · 19/02/2025
I am currently using Cursor to build a #elixirlang #phoenix application. It kept adding outdated package versions, so I decided to build an MCP server to solve this issue. If you are experiencing the same problem, give it a try: hex-mcp.9elements.com
hex-mcp.9elements.com
Hex MCP Server - Package Versions for AI Tools
Help AI tools like Cursor to automatically use the correct package versions when adding them to your Elixir projects.
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Daniel Hoelzgen @dhoelzgen.dev · 28/01/2025
Got my @elixirconfeu.bsky.social tickets, super excited to meet the #elixirlang folks in person!
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Claudio Ortolina @claudio-ortolina.org · 11/01/2025
#ElixirLang devs - what are you using for performance metrics? Telemetry + Prometheus + Grafana? StatsD + Datadog? Something else?
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Daniel Hoelzgen @dhoelzgen.dev · 10/01/2025
I am incredibly proud of the work of @molily.de and his team at @9elements.com, visualizing public health data on the WHO data hub. If you are into data visualization, this is certainly worth a look!
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Waseem @waseem-medhat.bsky.social · 08/12/2024
I thought it might be fun (and possibly helpful to others) to create a thread to document the things that I learned or used for the first time while doing AoC with Elixir. #adventofcode #elixirlang #myelixirstatus
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Daniel Hoelzgen @dhoelzgen.dev · 04/12/2024
Really happy to see my post about Phoenix LiveView session storage featured in the latest issue of the great @elixir-radar.com newsletter - This means a lot to me, thank you!
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Serg 🇺🇦 @chernata.com · 03/12/2024
Oh hell yes, I actually can't wait. This was my main gripe with #ElixirLang templates. github.com/phoenixframe...
github.com
Support {...} interpolation in body by josevalim · Pull Request #3514 · phoenixframework/phoenix_live_view
The first commit has the code changes. The second commit runs mix format to migrate the codebase, so you can see if you prefer the new style or not. cc @SteffenDE @chrismccord @connorlay @msaraiva
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Daniel Hoelzgen @dhoelzgen.dev · 03/12/2024
Phoenix LiveView 1.0 was just released by Chris McChord phoenixframework.org/blog/phoenix...
phoenixframework.org
Phoenix LiveView 1.0.0 is here! - Phoenix Blog
LiveView 1.0 is out!
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Daniel Hoelzgen @dhoelzgen.dev · 27/11/2024
Just did a short write-up on storing session data in a #LiveView application so that it survives page reloads and navigation events within the same live_session. 9elements.com/blog/robust-... #ElixirLang #ElixirPhoenix
9elements.com
Robust Session Storage in Phoenix Live View Sessions - 9elements
For an internal project called ‘ControlManiac’, which helps us with all the boring numbers juggling in our software studio, I had to add a global filter to the navigation bar, which lets me select the...
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Daniel Hoelzgen @dhoelzgen.dev · 25/11/2024
Planning which #ElixirLang conferences to attend next year? @jola.dev got you covered with a nice overview page
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Daniel Hoelzgen @dhoelzgen.dev · 13/11/2024
Seeing both the #Ruby and #ElixirLang starter packs grow makes me really happy. Thanks for keeping them up to date!
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Daniel Hoelzgen @dhoelzgen.dev · 12/11/2024
I am surprised at how bad ChatGPT is for Elixir, especially when comparing it to Ruby. Sure, I got some strange answers for Ruby, too, but for Elixir, both discussions with ChatGPT and CoPilot are so full of hallucinations that I currently just keep my hand off them completely.
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Daniel Hoelzgen @dhoelzgen.dev · 01/11/2024
Do you have recommendations for #Elixirlang books, courses, or posts that focus on functional programming patterns instead of the language / standard library itself?
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Chris, The 0.5x Engineer @llcoolchris.dev · 29/10/2024
Alright GANG #ElixirLang, what do we think about this pattern? See dev.to/martinthenth...
This is a screenshot of Elixir code that contains a with statement with chained clauses. It has a particular pattern where each clause is identified by an atom so that error handling is way easier!

Here is the code: 
with {:is_email, true} <- {:is_email, is_email_address?(email)},
     {:is_available, true} <- {:is_available, EmailAddresses.is_available(email)} do
  ...
else
  {:is_email, false} ->
    {:error, :bad_request}

  {:is_available, false} ->
    {:error, :conflict}
end
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Reposted by Daniel Hoelzgen
Joshua Wood @joshuawood.net · 19/10/2024
Reminder that I have a #Ruby and #RubyonRails starter pack here for anyone looking for their Ruby Friends. go.bsky.app/HD2Ty2o
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Daniel Hoelzgen @dhoelzgen.dev · 02/11/2023
Implementing a proper search function for a video-based app can be challenging. We used Whisper and GPT in a client’s Ruby on Rails application to query the actual content of the videos instead of user-provided descriptions, with excellent results. #ai #artificialintelligence #llm #gpt #openai
9elements.com
Enhancing video search &amp; discovery in a Rails application by using Whisper and ChatGPT - 9elemen...
Building a reliable search for a web application is hard. Building it for a video-based platform is even harder. For Medmile, a German platform offering bite-sized video courses for doctors, we relie...
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Daniel Hoelzgen @dhoelzgen.dev · 18/10/2023
To allow eager loading scoped associations that require a parameter in my #Ruby on #Rails #ActiveRecord models, I use a global store to provide the info I need. It's a bit clunky, but Preloaders would not allow chaining.
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Daniel Hoelzgen @dhoelzgen.dev · 15/10/2023
For a medical & caretaking project, I experimented with combining symbolic #logic with #LLMs to mitigate their tendency to nondeterministic behavior and #hallucinations. Still, it leaves a lot of work to be done, but it's a promising approach for situations requiring higher reliability.
medium.com
Using symbolic logic for mitigating nondeterministic behavior and hallucinations of LLMs
Combing LLMs and symbolic logic
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