Quick Reference

A fast lookup table of the utilities, hooks, and helpers already in this codebase - check here before writing a new one. Each entry links to the file that defines it; follow the links in the other docs pages for the full explanation.

Auth & access guards

Server-side (Server Components, Server Actions) - src/lib/auth-utils.ts:

Export	What it does
`requireAuth()`	Redirects to `/login` if there's no session; otherwise returns the session.
`requireAuthAndPremium(redirectUrl?)`	Like `requireAuth`, plus redirects if the user has no active Polar subscription. Skipped when Polar isn't configured.
`requireUnauth()`	Redirects signed-in users away from auth-only pages (login, signup) back to `/`.
`getSessionOnServer()`	Reads the session without redirecting; `null` when unauthenticated.
`requirePremiumUserFromRequest(req)`	Route Handler variant of `requireAuthAndPremium` - throws a 401/403 `Response` instead of redirecting.

Client-side:

Export	Where	What it does
`authClient`	`src/lib/auth-client.ts`	Better Auth React client - `signIn`, `signOut`, `useSession`, `checkout`, ...
`useCurrentUser()`	`src/features/user/hooks/use-user.ts`	Current user's profile (`trpc.user.me`).
`useHasActiveSubscription()`	`src/features/subscriptions/hooks/use-subscription.ts`	Standard client-side premium check; treats everyone as premium when Polar isn't configured. Use for UI gating only, not enforcement.
`useSubscription()`	`src/features/subscriptions/hooks/use-subscription.ts`	Raw Polar customer state. Prefer `useHasActiveSubscription` unless you need the raw data.

tRPC procedure builders (src/trpc/init.ts) - see Architecture:

Export	What it does
`baseProcedure`	Public, no auth.
`protectedProcedure`	Requires a session, throws `UNAUTHORIZED` otherwise. Attaches `ctx.auth`.
`premiumProcedure`	`protectedProcedure` + active subscription check, throws `FORBIDDEN` otherwise. Attaches `ctx.customer`.

Backend clients & services

Export	Where	What it does
`prisma` (default export)	`src/lib/db.ts`	Shared Prisma client. Always import this instead of `new PrismaClient()`.
`getRedis()`	`src/lib/redis.ts`	Shared Redis client, connects lazily on first call.
`redis` (default export)	`src/lib/redis.ts`	Raw client instance - may not be connected yet, prefer `getRedis()`.
`isPolarEnabled` / `polarClient`	`src/lib/polar.ts`	Whether billing is configured, and the Polar SDK client (`null` if not). Check the flag before using the client.
`isResendEnabled` / `resendClient`	`src/lib/resend.ts`	Whether transactional email is configured, and the Resend client (`null` if not).
`sendEmail({ to, subject, html })`	`src/lib/mailer.ts`	Sends via Resend, falls back to console-logging the email when Resend isn't configured.
`resetPasswordEmailHtml(...)` / `verifyEmailHtml(...)`	`src/lib/mailer.ts`	Pre-built HTML templates for the two auth emails.
`openrouter` / `AI_MODEL`	`src/lib/ai.ts`	Shared Vercel AI SDK provider and default chat model id, for `streamText`/`generateText`.
`getStreamContext()`	`src/lib/stream-context.ts`	Shared resumable-stream context for resumable AI chat responses.

tRPC (data fetching)

Export	Where	What it does
`useTRPC()`	`src/trpc/client.tsx`	Client components: get query/mutation options for `useQuery`/`useMutation`.
`TRPCReactProvider`	`src/trpc/client.tsx`	Root client provider (tRPC + React Query + IndexedDB persistence). Mounted once in `layout.tsx`.
`trpc` (options proxy)	`src/trpc/server.tsx`	Server Components: build the same query options as `useTRPC()`, for use with `prefetch`.
`caller`	`src/trpc/server.tsx`	Direct server-side procedure calls as plain async functions, no HTTP round-trip.
`prefetch(queryOptions)`	`src/trpc/server.tsx`	Prefetches a query into the request-scoped `QueryClient` from a Server Component.
`HydrateClient`	`src/trpc/server.tsx`	Wrap a subtree that used `prefetch` so the client tree gets the already-fetched data.
`makeQueryClient()`	`src/trpc/query-client.ts`	Factory for a correctly-configured `QueryClient`. Used internally by both providers above - rarely called directly.

Full walkthrough: Data Fetching.

Config

Export	Where	What it does
`env`	`src/config/env.ts`	Runtime-validated env vars (Zod). Always import this instead of reading `process.env` directly.
`PAGINATION`	`src/config/constants.ts`	Shared pagination defaults/limits (`DEFAULT_PAGE_SIZE`, `MAX_PAGE_SIZE`, ...).
`APP_NAME` / `APP_DESCRIPTION`	`src/config/constants.ts`	App-wide display name/description for titles, metadata, emails.

UI utilities

Export	Where	What it does
`cn(...inputs)`	`src/lib/utils.ts`	Merges Tailwind classes safely (resolves conflicts) via `clsx` + `tailwind-merge`. Use instead of string concatenation.
`useIsMobile()`	`src/hooks/use-mobile.ts`	Live viewport check below the 768px breakpoint. `false` during SSR - prefer CSS breakpoints unless you need a real JS conditional.
`useUIStore`	`src/stores/ui-store.ts`	Zustand store for cross-cutting UI state (currently: sidebar collapsed/expanded).

Shared components

Non-ui/ components in src/components/ - see Frontend for the full ui/ primitive list.

Component	What it does
`ConfirmDialog`	Standard "Are you sure?" dialog for ordinary, low-stakes deletes. Never wire a delete straight to a click.
`CriticalConfirmDialog`	Destructive/hard-to-reverse deletes - user must retype a confirmation string before confirming.
`AppShell`	Dashboard layout shell: sidebar + `EmailVerificationBanner` + content area. Wraps every `(dashboard)` page.
`AppSidebar`	Sidebar nav content rendered inside `AppShell`.
`EmailVerificationBanner`	Dismissible-by-verification banner shown while the signed-in user's email is unverified.
`LanguageToggle`	Locale switcher (`en`/`de`); persists the choice via a cookie-writing Server Action.

Details on the four required UI states (loading/empty/error/content) and confirm-dialog wiring: Frontend.

Quick Reference ​

Auth & access guards ​

Backend clients & services ​

tRPC (data fetching) ​

Config ​

UI utilities ​

Shared components ​

See also ​