# Development Experience

Local development uses two composable processes — the worker runtime and the client dev server — that run concurrently.

## What runs

```bash
npm run dev
```

The project template runs both processes via `concurrently`:

1. **`vite dev`** — Client dev server with HMR. Changes to Lit components reflect instantly in the browser. Configured in `vite.config.ts`.
2. **`bkper app dev`** — The worker runtime:
    - **Miniflare** — Simulates the single Cloudflare Worker locally.
    - **Cloudflare tunnel** — Exposes `/events` via a public URL so Bkper can route webhook events to your machine.
    - **File watching** — Server changes trigger automatic rebuilds via esbuild.

You can also run them independently: `npm run dev:client` for just the UI, or `npm run dev:server` for the local Worker.

## URLs

| Endpoint                               | URL                                         |
| -------------------------------------- | ------------------------------------------- |
| Client (Vite dev server)               | `http://localhost:5173`                     |
| Server Worker (Miniflare)              | `http://localhost:8787`                     |
| App API routes                         | `http://localhost:8787/api/*`               |
| App OpenAPI spec                       | `http://localhost:8787/openapi.json`        |
| Events (via tunnel to the same Worker) | `https://<random>.trycloudflare.com/events` |

The Vite dev server proxies `/api` requests to `http://localhost:8787` (configured in `vite.config.ts`). The app OpenAPI spec is served by the Worker at `http://localhost:8787/openapi.json`. The tunnel URL is automatically registered as the `webhookUrlDev` in Bkper, so events from books where you're the developer are routed to your local machine.

## Configuration flags

There is one local Worker. Override its port when needed:

```bash
bkper app dev --sp 8787
```

## Client configuration

The client dev server is configured in `vite.config.ts` at the project root. This is a standard Vite config — add plugins, adjust settings, or customize the dev server as needed.

### Local development authentication

During local development, the Vite dev server runs a Bkper auth middleware plugin (`createBkperAuthMiddleware()` from `bkper/dev`). This plugin:

1. Uses your CLI credentials (from `bkper auth login`) to obtain and refresh OAuth tokens
2. Injects the token into your client code automatically
3. Proxies `/api` requests to the Miniflare worker

Before starting development, run:

```bash
bkper auth login   # one-time setup
```

Then `npm run dev` handles authentication automatically. The client calls `auth.getAccessToken()` and the middleware ensures the token is valid.

When your client calls an app server route under `/api/*`, include that token as `Authorization: Bearer <token>` to match production dispatch behavior. Local outbound uses your CLI credentials when the app server or event handler calls Bkper.

If you see authentication errors in the browser, verify you're logged in:

```bash
bkper auth token   # should print a token
```

This is the canonical pattern for local development. Do not manually pass tokens or implement custom auth flows.

## Local secrets

Environment variables for local development live in a `.dev.vars` file at the project root:

```bash
# .dev.vars (gitignored)
EXTERNAL_SERVICE_TOKEN=your-token-here
```

Copy from the provided template:

```bash
cp .dev.vars.example .dev.vars
```

These variables are available as `c.env.SECRET_NAME` in your Hono handlers during development.

## KV storage

KV data persists locally in the `.mf/kv/` directory during development. This means your data survives restarts — useful for testing caching and state patterns.

```ts
// Read
const value = await c.env.KV.get('my-key');

// Write with TTL
await c.env.KV.put('my-key', 'value', { expirationTtl: 3600 });
```

See the [Cloudflare KV documentation](https://developers.cloudflare.com/kv/) for more usage patterns.

## Type generation

The `env.d.ts` file provides TypeScript types for the Worker environment — KV bindings, secrets, and other platform services. It's auto-generated based on your `bkper.yaml` configuration and checked into version control.

Rebuild it after changing services or secrets in `bkper.yaml`:

```bash
bkper app build
```

## The development loop

1. Run `npm run dev`
2. Edit client code — see changes instantly via Vite HMR
3. Edit server code — auto-rebuilds and reloads via esbuild watch
4. Trigger events in Bkper — your local Worker receives them at `/events` via the tunnel
5. Check the activity stream in Bkper to see handler responses
6. Iterate

## Debugging

- **Server errors** — Check the terminal output from `bkper app dev`. Worker runtime errors appear here.
- **Event handler errors** — Check the Bkper activity stream. Click on an event handler response to see the result or error, and replay failed events.
- **Client errors** — Use browser DevTools. The Vite dev server provides source maps.