Editing code you don't understand is how subtle regressions ship. pstack gives you four ways in. /how explains what the code does now. /why digs up the reasons it's shaped that way. /teach blends both into one explanation. /recall rebuilds your own recent context on a topic.
/how do we dedupe notifications? is there an n+1 when we look up subscribers?
Ask the question you actually have. /how reads the code and answers at the level of a senior engineer onboarding you onto the subsystem, with the runtime flow, the key types, and the non-obvious parts. For a big subsystem it fans out two to four read-only explorers first. For a narrow question it just reads and explains.
/how can also push back on the design. Ask for Critique mode when you suspect the structure itself:
/how explain the sync service, then critique its ownership boundaries
The explanation comes first, so the critique stays grounded in how the thing really works.
/why was the retry limit set to five? does the reason still hold?
/why works like a detective on a cold case. It starts from source control, then queries whatever evidence categories your MCPs expose, such as the issue tracker, long-form docs, team chat, observability, error tracking, and analytics, all in parallel. The report cites everything, separates direct evidence from inference, and says "appears to" when the record is thin. A null result gets reported too, because "nobody wrote down why" is itself an answer.
The two compose naturally. do why first then how is a perfectly good prompt when you suspect the history explains the mess.
/teach me how this PR changes retries. convince me it fixes the cause and not the symptom.
/teach is for when a summary isn't enough. It runs /how and /why, for a small change maybe just one of them, and weaves the findings into a plain explanation that builds up diagram by diagram. The "convince me" framing is worth stealing. It turns the explanation into an argument you can poke at instead of a tour.
/recall catch me up on the export work from last week
/recall mines your own recent chats plus the shared record (issues, prior fixes, errors still firing) and hands back a brief on where things stand and what's next. Use it when you're returning to a topic cold. If you want to resume one specific chat, that's the Session pickup playbook below, not /recall.
When another agent (or you, last week) left a branch mid-flight:
/poteto-mode take over this branch. read the decision log, figure out what's done, and continue from there. don't redo finished work.
The Session pickup playbook treats the prior trail as authoritative. It reconstructs the branch state and decisions, names the resume point, and verifies inherited claims against the original goal instead of re-deriving everything from scratch.
Pitfall: don't skip this page's skills because "the agent will read the code anyway." An agent that starts editing without a traced model tends to fix the symptom at the first plausible spot. /how first is cheaper than the second bug.
Next: Design the change.