Your First App

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With Slim and a PSR-7 implementation installed, you're ready to write the smallest possible Slim application: a public/index.php file that bootstraps the app, defines one route, and runs.

The Minimal index.php

Open public/index.php (create it if it doesn't already exist) and add this:

<?php
require __DIR__ . '/../vendor/autoload.php';

use Slim\Factory\AppFactory;

$app = AppFactory::create();

$app->get('/', function ($request, $response, $args) {
    $response->getBody()->write("Hello, Slim!");
    return $response;
});

$app->run();

Note: This code is a correct, static Slim example for you to copy into your own Slim project — this tutorial site has no Composer/Slim installed, so nothing here executes live on this page.

Line-by-Line Walkthrough

Line	What it does
`require __DIR__ . '/../vendor/autoload.php';`	Loads Composer's autoloader so every class from Slim and its dependencies becomes available without manual `require` statements.
`use Slim\Factory\AppFactory;`	Imports the `AppFactory` class so it can be referenced simply as `AppFactory` instead of the full namespace.
`$app = AppFactory::create();`	Builds the Slim application object. Internally it picks a PSR-7 implementation (the one you installed, e.g. `slim/psr7`) automatically.
`$app->get('/', function (...) {...});`	Registers a route: when a `GET` request hits `/`, the closure runs.
`$response->getBody()->write(...);`	Writes text into the outgoing response body.
`return $response;`	Every route handler must return the response object — this is how Slim knows what to send back.
`$app->run();`	Starts Slim: it matches the incoming request against your routes and sends the response. This call must always be last in the file, after every route has been defined.

Running It Locally

From your project's root folder (the one containing public/ and vendor/), start PHP's built-in server:

php -S localhost:8080 -t public

Now open http://localhost:8080 in a browser. You should see Hello, Slim! printed on the page. If you instead see a blank page or an error, double-check that vendor/autoload.php exists (meaning Composer install succeeded) and that you started the server with -t public so it serves from the correct folder.

Next steps: Now that a single route works, move on to Routing Basics to learn about all the HTTP verbs Slim supports.

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