You’re testing a new feature in a development environment. You click “Submit,” and a few seconds later, your phone buzzes with a real-world SMS notification. Or worse, a real customer receives a “Test” email meant for a sandbox user. While these aren’t usually “delete-the-database” disasters, they represent a fundamental failure in application guardrails…

#programming #javascript

https://lackofimagination.org/2026/03/beyond-the-readme-enforcing-application-guardrails-at-runtime/

We’ve all had that sinking feeling. There are multiple crash reports from production. We have the exact input parameters that caused the failures. We have the stack traces. Yet, when we run the code locally, it works perfectly. If we could simply rewind time and watch the code execute exactly as it did for those failed requests, life would be a lot easier…

#programming #javascript

https://lackofimagination.org/2026/02/time-travel-debugging-replaying-production-bugs-locally/

In a typical imperative application, business logic and side effects are inextricably linked. For example, when you write await db.checkInventory(…), the runtime immediately reaches out to the database. Our Effect System works differently. When our code needs to check inventory, it doesn’t call the database; it returns a plain object instead, which will be executed later by an interpreter.

#programming #javascript

https://lackofimagination.org/2025/12/testing-side-effects-without-the-side-effects/

If you look at the source code of a typical application, you will likely find business logic tangled with database calls, HTTP requests firing off in the middle of validation rules, and try/catch blocks sprinkled here and there. The biggest casualty of this coupling is testability…

#programming #javascript

https://lackofimagination.org/2025/11/managing-side-effects-a-javascript-effect-system-in-30-lines-or-less/

Studies have shown that expecting to teach a subject improves how well you learn and remember it. By writing your work as if you're teaching it, you're tricking your brain into going deeper and organizing your knowledge better.

https://www.svendewaerhert.com/blog/higher-education/

Companies break promises all the time. A self-guaranteeing promise does not require you to trust anyone. You can verify a self-guaranteeing promise yourself.

File over app is a self-guaranteeing promise. If files are in your control, in an open format, you can use those files in another app at any time. Not an export. The exact same files.

https://stephango.com/self-guarantee

Anytime you rely on an LLM to enforce something important, you will fail. Whenever you find yourself dealing with an LLM-based system, you can always find a way to shift the complexity to a tool to avoid that issue. As an example, if you want to do algebra with an LLM, the solution is not asking the LLM to directly perform algebra, but instead providing a tool capable of algebra to the LLM, and then relying on the LLM to call that tool with the proper parameters.

https://lethain.com/what-can-agents-do/