I used the following prompt excerpted from Simon Willison’s excellent commentary to build a linear walkthrough of Nextmini, a fairly complex codebase built in Rust. Unsurprisingly, Codex launched several subagents to scout different parts of the codebase without any additional hints on spawning subagents.
Read the source and then plan a linear walkthrough of the code that explains how it all works in detail.
Then run “uvx showboat —help” to learn showboat - use showboat to create a walkthrough.md file in the repo and build the walkthrough in there, using showboat note for commentary and showboat exec plus sed or grep or cat or whatever you need to include snippets of code you are talking about.
The command-line utility, showboat, doesn’t need a skill, since showboat --help is so comprehensive that the agent can understand how to use it just by reading the help.
The entire session takes 9 minutes 41 seconds to complete with GPT 5.3 codex xhigh, which is suprisingly fast to me.