# Introduction

> Tetsu is an HTTP framework for Bun with controllers, lifecycle hooks in fixed slots and types inferred from end to end.

Tetsu is an HTTP framework for Bun. Controllers get their dependencies as function arguments, hooks run in fixed slots instead of a middleware chain, and the compiler infers every type from the path to the handler. There are no decorators, no DI container and no dependencies in the core.

```ts
import { controller, createApp, httpError, route } from "@tetsujs/core";
import { z } from "zod";


const users = controller("Users", ({ repo }: { repo: UserRepository }) => ({
  get: route({
    method: "GET",
    path: "/users/:id",
    schema: { params: z.object({ id: z.coerce.number() }) },
    handler: (ctx) => {
      const user = repo.find(ctx.params.id);
      if (!user) throw httpError(404, "USER_NOT_FOUND");
      return user;
    },
  }),
}));


Bun.serve({ ...createApp({ routes: users({ repo }) }) });
```

Nothing here is annotated. `ctx.params.id` is a number because the schema converts the path segment, and without `:id` in the path it would not exist. A request with a bad id gets a `422` and never reaches the handler.

## What it is not

Tetsu runs on Bun only. It has no plugin system: a package such as CORS or rate limiting is a hook, mounted like your own. It has no container, no file-based routing and no global registry: what runs for a route is declared in code, on the route, its groups or the application.

## Where to go next

* [Installation](/docs/installation/) — requirements and TypeScript settings.
* [Quick start](/docs/quick-start/) — a first application with a test.
* [Key concepts](/docs/key-concepts/) — the whole model on one page.