Maintaining an organizational knowledge graph with an LLM and event sourcing Organizations are surprisingly good at forgetting. Decisions are made on calls, insights get buried in Slack threads, and a month later no one remembers why things are the way they are. At Arkency, I had a feeling that some...

3 example process managers in Rails I am writing this blogpost from this beautiful place in the Polish mountains. Our RailsEventStore camp takes place this week. Process managers are meant to map business process into code. The more readable and declarative it is, the better the chance domain expert...

Ingress is not the owner of the invariant A polemic with Callbacks Are Not Invariants by Brandon Weaver. A disclaimer: I’m a RailsEventStore maintainer and this article ends up on the Arkency blog — so cards are on the table. Despite this, I’m keeping the core of my argument in pure ActiveRecord: no...

Let Your AI Assistant Explore the Event Store with res-mcp When you’re debugging with an AI assistant, half the work is giving it enough context. You copy event payloads into the chat, paste stream contents, look up IDs, then repeat the process every time you need another piece of information. ruby_...

Inspect Your Event Store From the Terminal With the res CLI Because not every debugging session needs rails c. Most event store debugging starts the same way: you open a Rails console, try to remember the Event Store read API, and type something like: event_store.read.stream("Order$123").to_a It wor...

What’s New in Rails Event Store 3.0 Rails Event Store 3.0 is primarily a cleanup release. Throughout the 2.x series we introduced new features while gradually deprecating APIs we no longer wanted to maintain. In 3.0, those deprecated APIs are finally gone. There are no major new concepts or APIs to ...

Storing data as a sequence of events - RubyConfAt lightning talk supplement This post originated from the lightning talk and the discussions I had afterward at RubyConfAt. It was a great conference. Especially the music part was amazing. Big kudos and applause to the organizers, once again! The Ligh...

RailsEventStore 2.19: Starting Gun for 3.0 RailsEventStore 2.19.1 is out — grab that one, not 2.19.0 (more on why below). This release is the starting gun for 3.0. We’ve added deprecation warnings for everything we’re removing in the next major version. Run your test suite — every warning you see is...

The Rails Way in 2026 We had an interesting discussion at the Arkency weekly call today. The topic was how to define “the Rails Way” in 2026. The discussion branched in many directions, but I want to capture the result here. We get to see a lot of Rails repositories. There’s a pattern that shows up ...

Rails apps have layers but no modules You can have 200 models and zero modules. That’s the problem with typical Rails conventions. Rails supports layers - models, views, controllers. But layers are not modules. Within one layer - especially models - usually all is mixed together. There are no bounda...

Getting nondeterministic agent into deterministic guardrails AI agents don’t reliably follow your instructions. Here’s how I made it hurt less. My context: I currently work on a 12-year-old Rails legacy code base The code base is undergoing modernization. Some of the large Active Record classes have...

The timezone bug that hid in plain sight for months We recently fixed a bug in a financial platform’s data sync that had been silently causing inconsistencies for months. The bug was elegant in its simplicity: checking DST status for “now” when converting historical dates. The broken code I found th...

Stop using DateTime in 2026 (unless you work for UNESCO) DateTime has been considered deprecated in Ruby since 3.0. It’s 2026. Why are people still using it? During a recent code review, we found this: whatever.starts_at = DateTime.now When asked why DateTime instead of Time, the response was: “Date...

Adding multi-tenancy to a DDD Rails app Many businesses when they set out to create some software they need, don’t know that one day, they might need multi-tenancy. This is one of the features, that is not easy for programmers to add later easily. It might take months or even years. Let me describe ...

Rewrite with Confidence: Validating Business Rules Through Isolated Testing A few months back, our team at Arkency faced a challenge that many Rails developers might recognize. We needed to implement a new flow at Lemonade that would eventually replace a legacy process — but with three major constra...