Secrets live on a keychain and are exposed only to the specific secrets a tool asks for, only open-source tools may request secrets at all, and if the package code changes, the installation is void until you re-approve. That last rule closes the supply-chain hole that every tool registry has — a package you vetted quietly updating underneath you and inheriting the credentials you already granted. It costs convenience on every update, and it is the correct trade for anything holding a database password.
Superuser hosts tools rather than being one. Every package published there becomes its own server with its own address, so there is no single endpoint or global tool list.
Whatever you or someone else publishes, plus their first-party toolkits — Postgres, image generation, search through Exa and Perplexity, Wikipedia, weather and YouTube among the documented examples. Tools published there can be used outside Superuser too.
An account and a secret token. Person-to-person chat is free; agents are a monthly subscription with per-token overage, and hosted tool execution is billed by compute time.