Explain a large repository
Drop into an unfamiliar codebase and ask. Pier maps the structure, the key modules, and how a request flows through the system.
❯ I just cloned this repo. What is it, and where does an order get charged?
● Let me map the project before answering.
● Ran rg --files -g '*.go' | head
└ cmd/server/main.go
internal/checkout/handler.go
internal/payments/stripe.go
internal/orders/repo.go
● It's a Go checkout service: an HTTP server (cmd/server) over three domains: checkout, payments, orders.
● An order is charged in internal/payments/stripe.go:Charge, called from checkout/handler.go once the cart validates. Want me to walk that path?
❯ Ask Pier anything… (/ for commands)
- 01Open the repo and ask what it does or where a feature lives.
- 02The agent builds a map of modules, dependencies, and conventions.
- 03It answers with the specific files and call paths that matter.
- 04Follow up in the same session as you go deeper.
Onboarding onto a new codebase is mostly reading. You clone the repo, open the entry point, and start the slow work of building a mental map: which package owns what, how a request flows, where the surprising bits are hidden. It is the least glamorous part of joining a team or inheriting a project, and it can eat days. Pier reads it the way you would, then gives you the short version: what the major pieces are, how they fit together, and where to start for the change you have in mind.
What makes it useful is that you can keep going. The first answer gets you pointed in the right direction, and the follow-ups take you deeper. Ask where authentication is enforced, why two modules both reach for the database, or what would break if you changed a shared type, and it follows the real call paths to answer with specific files and line numbers instead of a hand-wavy summary. It feels like asking someone who has already read the whole thing.
Asking questions about a repo costs almost nothing, since the agent is reading rather than writing. You can poke around for an afternoon and barely move the meter. The pricing page has the rates if you want to check.