# AGENTS.md - this project

Instructions for AI coding agents working in this repository.

## Project

A Next.js (App Router) + Tailwind CSS v4 + shadcn/ui + Vercel AI SDK + Zod validation project.

Stack: Next.js (App Router), Tailwind CSS v4, shadcn/ui, Vercel AI SDK, Zod validation.

## Commands

- Dev server: `npm run dev`
- Production build (also type-checks): `npm run build`
- Lint: `npm run lint`
- Add a component: `npx shadcn@latest add <component>`

## Project structure

- `app/` holds routes: `page.tsx`, `layout.tsx`, `loading.tsx`, `error.tsx`, `route.ts` for API handlers.
- Shared UI in `components/`, server-only helpers in `lib/` (mark them with `import "server-only"`).

## How to work in this repo

- Read the relevant files before editing. Follow the patterns already in the codebase over these generic rules.
- Make the smallest change that solves the task. Do not refactor or reformat unrelated code.
- Before saying a task is done, run the type-check, lint and tests listed under Commands and fix what you broke.
- If requirements are ambiguous, ask one clear question instead of guessing.
- Never commit secrets, API keys or `.env` files. Use env vars and keep `.env.example` up to date.
- Do not add a new dependency when the standard library or an existing dependency already covers it.
- Ask before adding, removing or upgrading any dependency.
- Ask before changing database schemas, auth, payments or CI configuration.
- Never delete files, drop data or run destructive commands (`rm -rf`, `git push --force`, `DROP TABLE`) without explicit approval.
- Keep each change under ~200 changed lines where possible; split larger work into steps.

## Next.js (App Router)

- Check the Next.js major version in `package.json` before using an API; follow the docs for that version.
- Components are Server Components by default. Add `"use client"` only to the smallest leaf component that needs state, effects, or browser APIs.
- Fetch data in Server Components or Server Actions, not in `useEffect`.
- In Next.js 15+, `params`, `searchParams`, `cookies()` and `headers()` are async: always `await` them.
- Mutations go through Server Actions (`"use server"`) or `route.ts` handlers. Validate every input on the server and re-check auth inside the action.
- After a mutation, call `revalidatePath()` or `revalidateTag()` instead of forcing the whole route dynamic.
- Use `next/image` for images, `next/font` for fonts and `next/link` for internal links.
- Export `metadata` or `generateMetadata` from every page for title, description and Open Graph tags.
- Only variables prefixed `NEXT_PUBLIC_` reach the browser. Never put secrets in them.
- In Next.js 16, `middleware.ts` is renamed `proxy.ts`. Use whichever file the project already has.

## Tailwind CSS v4

- Tailwind v4 is configured in CSS: `@import "tailwindcss";` plus `@theme { ... }` for design tokens. Do not create a `tailwind.config.js` unless the project already has one.
- Use theme tokens (colors, spacing) instead of arbitrary values like `w-[37px]`.
- Build responsive layouts mobile-first with `sm:`, `md:`, `lg:` prefixes.
- Extract repeated class lists into components, not `@apply` chains.
- Support dark mode with the `dark:` variant when the project uses it.

## shadcn/ui

- Before building a UI primitive, check whether a shadcn/ui component exists and add it with `npx shadcn@latest add <component>`.
- Components live in `components/ui/` and are owned code: customize them there rather than wrapping them in more layers.
- Merge class names with the `cn()` helper from `lib/utils`.
- Keep accessibility props from Radix (labels, `aria-*`, focus handling) intact.

## Vercel AI SDK

- Check the installed `ai` package major version; tool and message APIs changed between majors.
- Call models only from server code (route handlers or Server Actions). API keys never reach the browser.
- Stream long responses with `streamText`; use `generateObject`/structured output with a Zod schema when you need JSON.
- Define tools with `tool()` and a Zod input schema; validate and authorize inside each tool before acting.
- Keep model IDs in one config module so they can be swapped without hunting through the code.
- Set `maxOutputTokens`/step limits and handle errors and aborts in the UI.

## Zod validation

- Validate all untrusted input (request bodies, form data, env vars, third-party API responses) with a Zod schema at the boundary.
- Derive TypeScript types from schemas with `z.infer<typeof schema>`; do not hand-write duplicate types.
- Use `safeParse` where you need to return validation errors to the user.

## Avoid

- Do not add `"use client"` to layouts or pages just to silence an error; move the interactive part into a child component.
- Do not use the Pages Router (`pages/`) APIs such as `getServerSideProps` in an App Router project.

## Reference docs

- [Next.js docs](https://nextjs.org/docs)
- [Tailwind CSS docs](https://tailwindcss.com/docs)
- [shadcn/ui docs](https://ui.shadcn.com/docs)
- [AI SDK docs](https://ai-sdk.dev/docs)
- [Zod docs](https://zod.dev)