Understanding a Codebase

Select a feature and press K to open Learning Mode. It is a read-only reader for the project's code with an agent attached: browse the files, point at the part you don't understand, and ask about it. Nothing in Learning Mode changes your files. The only key that can lead to an edit is S, which hands the answer to an ordinary agent session and says so.

If you don't know where to start, you don't have to. On a project you have not asked anything about yet, the file list opens on a pinned Start here group: a ready-made question asking for a tour of the whole project, followed by whichever of the README, the contribution guide, the entry point, and the manifest that project actually has. Press t at any time for starter questions ("Explain this line by line", "What would break if I deleted this?") that load into the prompt so you can edit them before asking.

Learning Mode's file pane open on the pinned Start here group, with the read-only banner across the top — The pinned Start here group, and the permanent read-only header.

Asking a question

Point at what you want to ask about with f (the whole file), v (start a line range), P (the whole project), or x (the change under the cursor, in branch-changes scope). Then ask one of two ways:

Key	Asks for
`e`	Explain this to me — a teaching answer; no change is proposed
`c`	Ask for a change — a concrete proposal you can act on later

Answers are written for a newcomer by default — terms defined on first use, ending with what to read next — and L switches to familiar for denser answers.

Learning Mode showing src/main.rs open in the file pane, with the Questions pane on the right prompting to press e or t — Pointing at a file with `f`, ready to ask about it with `e` or `c`.

Acting on an answer

Key	Action
`F`	Ask a follow-up; the agent keeps the question and answer you just read
`D`	Ask again with the repository readable — slower, but it checks
`i`	Re-file the entry as the other kind; the answer text is left alone
`a`	Keep the answer as a to-do on this feature's TODO list
`S`	Hand it to a live agent session, with the prompt filled in and unsent

D is worth knowing about: an ordinary answer only sees the code on screen, so it can name files or line numbers that don't exist. D re-asks the same question with the repository open and keeps both answers so you can read them against each other. Codex is the exception — it has no way to answer without reading the repository, so every Codex answer already read it.

An answered Learning Mode question with the action footer showing F ask a follow-up, D ask again reading the repo, a keep as a to-do, and S escalate — An answered question, with the follow-up, re-ask, keep-as-TODO, and escalate actions in the footer.

Questions and answers are kept per project, so reopening K brings back what you asked before. Press ? inside Learning Mode for the full key list.