Content about #Ruby

Kobako is a sandbox I recently built on WebAssembly and mruby for the Ruby ecosystem, in support of Harness Engineering, to fill the gap where AI-written code has no safe environment to run in.

I already introduced Kobako’s design in a previous post, so this time I want to talk about performance. In its early versions, the Cold Start (the initial startup) took roughly 500 ms. That’s a lot slower than the 200 ms response time you’d usually aim for as a best practice. Even though AI generally tolerates slower responses, this isn’t about waiting on an LLM, so it still deserves to be judged by traditional API standards.

Developing Kobako has surfaced quite a few interesting cases. Continuing from the previous post, Building Kobako with AI: Will It Eventually Crash?, I ran into yet another new problem afterward—and this time it was the Segmentation Fault error I had always dreaded seeing during development. That signals a high chance something went wrong in the non-Ruby territory between Rust and WebAssembly.

Last week I published Kobako: Letting Agents Safely Operate Rails, introducing the goals of the Kobako gem. Since then I’ve kept pushing development forward with Claude Code—but I quickly ran into a situation that demanded major changes. Is this simply the fate of developing with AI?

This is a question worth discussing: when using AI to assist development, is the problem that AI isn’t capable enough, or that the design we humans handed it was too poor?

At RubyKaigi 2026 this year, while chatting with friends about Harness Engineering and the Sandbox aspect of it, I realized that Ruby still lacks a solid solution in this space. On the second night, I happened to be assigned to the druby (Ruby’s built-in distributed object system) group at the Code Party — and that’s how the idea for Kobako was born.

Recently, the Hono framework launched the Hono CLI tool, and I quickly created a Hono Plugin for Claude Code, adding Agent Skill support for querying documentation using Hono CLI.

At the same time, I realized that the ri (Ruby Information) command, which I rarely use, provides similar capabilities to the Hono CLI. Therefore, I created the Ruby Plugin ahead of schedule to provide the ri skill.

Recently, due to work-related reasons, I took a moment to revisit Open Policy Agent and discovered that the Cedar Language introduced by AWS is more suitable for implementing a policy mechanism similar to AWS IAM in software applications. Since it is built on Rust, I decided to try writing an extension in Rust so that it can be utilized in Ruby.

mruby compiles source code using a compiler (usually mrbc), resulting in a binary file in the mrb format. This file format is called RITE, and in order to execute compiled mruby code, it needs to be parsed and read.

The Form Object is a common pattern in Rails when our form becomes complex. But the tutorial in network’s example usually incapable of Rails’ form helper.

And I start thinking about is it possible to support form helpers without too many changes?

A few years ago, I have a post talking about Autoloading. In recent days, my colleague has some problems with Autoloading and Reloading.

Therefore I decided to review the Autoloading mechanism in Rails 5 and 6.

Include me, write test is many people’s nightmare. Many junior programmers feel it is hard to define which should be tested. So, I decided to share my experience after I tech my colleague today.