How to Include Composer Packages in Plain PHP Projects (Autoload + Example)

I used to avoid Composer in “plain PHP” projects because I thought it was only for frameworks. Then I needed a small library (a subtitle converter) for a simple PHP script and tried the old-school approach: downloading random ZIP files, copying folders around, and manually requiring files.

It worked… until it didn’t. One missing file, one wrong include path, and suddenly I was stuck in “Class not found” hell.

That’s when I switched to Composer properly—and the fix was surprisingly simple: install the package with composer require, then load vendor/autoload.php once. After that, the package works like magic in a plain PHP project.

What Composer does in a plain PHP project (quick explanation)

Composer is a dependency manager for PHP. It downloads libraries into a vendor/ folder and generates an autoloader file (vendor/autoload.php) so you don’t have to manually include every class file.

Framework or no framework—Composer works the same.

Step 1: Make sure Composer is installed

On your server or local machine, check:

composer --version

If you see a version number, you’re good. If not, install Composer first (I usually install it globally so it’s available anywhere).

Step 2: Create your project folder

I like to start clean:

mkdir my-plain-php-project
cd my-plain-php-project

Create a basic entry file:

touch index.php

Step 3: Install a Composer package (composer require)

In your original example, the package was a subtitle converter:

composer require mantas-done/subtitles

After this, Composer will create (or update) these things inside your project:

• composer.json (your dependency list)
• composer.lock (locked versions for consistent installs)
• vendor/ directory (downloaded packages)
• vendor/autoload.php (the autoloader file you must include)

Step 4: Include vendor/autoload.php (this is the missing piece)

This is the part most people forget in plain PHP projects. If you don’t load the autoloader, PHP won’t know where the package classes live.

Open your index.php and add:

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

Why I use __DIR__: it prevents path problems when your script runs from a different working directory.

Step 5: Use the package (real working example)

Now you can use the library normally. Example: convert an .srt file to .vtt:

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

use Done\Subtitles\Subtitles;

// Convert subtitles.srt → subtitles.vtt
(new Subtitles())->convert('subtitles.srt', 'subtitles.vtt');

echo "Done! Converted to VTT.";

Put your subtitle file in the same folder as index.php (or use full paths), then run:

php index.php

Common mistakes (and quick fixes)

1) “Failed to open stream: vendor/autoload.php”

• You didn’t run composer install / composer require in this project folder.
• Your script is inside a subfolder (example: public/index.php), so the path should be __DIR__ . '/../vendor/autoload.php'.

2) “Class not found”

• Autoloader is not included (add require __DIR__ . '/vendor/autoload.php';).
• Namespace/class name is wrong (double-check the package docs).

3) “It works locally but not on the server”

Most of the time, it’s because you uploaded your project without the vendor/ folder. Best practice is:

• Upload composer.json and composer.lock
• Then run composer install --no-dev on the server

Bonus: Autoload your own PHP classes (PSR-4 style)

Once I started using Composer, I also stopped manually requiring my own class files. Here’s the clean approach:

• Create a folder: src/
• Put your classes in there with namespaces
• Add an autoload rule in composer.json

Example composer.json snippet:

{
  "require": {
    "mantas-done/subtitles": "^1.0"
  },
  "autoload": {
    "psr-4": {
      "App\\": "src/"
    }
  }
}

Then regenerate the autoloader:

composer dump-autoload

Now you can use your own classes like use App\MyClass; without writing a bunch of require statements.

Final thoughts

If you remember only one thing: installing the package is not enough—you must include the autoloader. Once you add require __DIR__ . '/vendor/autoload.php'; at the top of your entry file (or a shared bootstrap.php), Composer packages work perfectly in plain PHP projects.