diff --git a/README.md b/README.md
index a284824..da68bbe 100644
--- a/README.md
+++ b/README.md
@@ -2,6 +2,33 @@
 
 A GitHub action for testing Solidus extensions
 
+## Inputs
+
+| Input | Description | Required | Default |
+|-------|-------------|----------|---------|
+| `ruby-version` | Ruby version to use | Yes | `3.3` |
+| `rails-version` | Rails version to use | Yes | `7.2` |
+| `solidus-branch` | Solidus branch to use | Yes | `main` |
+| `database` | Database to use (`sqlite`, `postgresql`, `mysql`, or `mariadb`) | Yes | `sqlite` |
+
+## Database Services
+
+This is a composite GitHub Action, which means it **cannot define services directly**. If you need to test against PostgreSQL or MySQL/MariaDB, you must define the database service in your workflow file.
+
+The action will install the necessary database client libraries automatically based on the `database` input.
+
+### Database Credentials
+
+The action automatically sets the correct `DB_USERNAME` based on the database:
+
+- **PostgreSQL**: `postgres` (default superuser)
+- **MySQL/MariaDB**: `root` (default superuser)
+
+Configure your database services with passwordless access for simplicity (see example below).
+
+> [!WARNING]
+> Rails 8.0 has a [known issue](https://github.com/rails/rails/issues/53673) with MySQL/MariaDB that causes empty `Mysql2::Error` messages. Until a fix is released, exclude the `mariadb` + Rails 8.0 combination from your test matrix.
+
 ## Example configuration
 
 ```yaml
@@ -26,6 +53,29 @@ jobs:
   rspec:
     name: Solidus ${{ matrix.solidus-branch }}, Rails ${{ matrix.rails-version }} and Ruby ${{ matrix.ruby-version }} on ${{ matrix.database }}
     runs-on: ubuntu-24.04
+    services:
+      postgres:
+        image: postgres:16
+        env:
+          POSTGRES_HOST_AUTH_METHOD: trust
+        options: >-
+          --health-cmd="pg_isready"
+          --health-interval=10s
+          --health-timeout=5s
+          --health-retries=5
+        ports:
+          - 5432:5432
+      mysql:
+        image: mysql:8
+        env:
+          MYSQL_ALLOW_EMPTY_PASSWORD: "yes"
+        options: >-
+          --health-cmd="mysqladmin ping"
+          --health-interval=10s
+          --health-timeout=5s
+          --health-retries=5
+        ports:
+          - 3306:3306
     strategy:
       fail-fast: true
       matrix:
diff --git a/action.yml b/action.yml
index ef79047..22c0056 100644
--- a/action.yml
+++ b/action.yml
@@ -11,89 +11,76 @@ inputs:
     required: true
     default: main
   database:
-    description: Database to use. sqlite3, postgresql, or mariadb
+    description: Database to use. sqlite, postgresql, mysql, or mariadb
     required: true
-    default: sqlite3
+    default: sqlite
   ruby-version:
     description: Ruby version to use
     required: true
     default: "3.3"
 
-services:
-  postgres:
-    image: postgres:latest
-    env:
-      POSTGRES_USER: solidus_user
-      POSTGRES_PASSWORD: password
-      POSTGRES_DB: solidus_extension_test
-    ports: ["5432:5432"]
-    options: --health-cmd pg_isready --health-interval 10s --health-timeout 5s --health-retries 5
-  mariadb:
-    image: mariadb:latest
-    ports: ["3307:3306"]
-    env:
-      MARIADB_USER: solidus_user
-      MARIADB_PASSWORD: password
-      MARIADB_DATABASE: solidus_extension_test
-      MARIADB_ROOT_PASSWORD: password
-    options: --health-cmd="mariadb-admin ping" --health-interval=10s --health-timeout=5s --health-retries=5
-
 runs:
   using: "composite"
   steps:
-  - uses: actions/checkout@v4
-  - name: Set up Ruby
-    uses: ruby/setup-ruby@v1
-    env:
-      RAILS_VERSION: ${{ inputs.rails-version }}
-      SOLIDUS_BRANCH: ${{ inputs.solidus-branch }}
-    with:
-      ruby-version: ${{ inputs.ruby-version }}
-      bundler-cache: true
-      cache-version: ${{ inputs.rails-version }}-${{ inputs.solidus-branch }}-{{ inputs.database }}-{{ inputs.ruby-version }}
-      rubygems: "latest"
-  - name: Restore apt cache
-    id: apt-cache
-    uses: actions/cache@v4
-    with:
-      path: /home/runner/apt/cache
-      key: ${{ runner.os }}-apt-${{ inputs.database }}
-      restore-keys: |
-        ${{ runner.os }}-apt-
-  - name: Install libvips
-    shell: bash
-    run: |
-      mkdir -p /home/runner/apt/cache
-      sudo apt update -qq
-      sudo apt install -qq --fix-missing libvips -o dir::cache::archives="/home/runner/apt/cache"
-      sudo chown -R runner /home/runner/apt/cache
-  - name: Install Postgres headers
-    if: inputs.database == 'postgresql'
-    shell: bash
-    run: |
-      mkdir -p /home/runner/apt/cache
-      sudo apt update -qq
-      sudo apt install -qq --fix-missing libpq-dev -o dir::cache::archives="/home/runner/apt/cache"
-      sudo chown -R runner /home/runner/apt/cache
-  - name: Install MariaDB headers
-    if: inputs.database == 'mariadb'
-    shell: bash
-    run: |
-      mkdir -p /home/runner/apt/cache
-      sudo apt update -qq
-      sudo apt install -qq --fix-missing libmysqlclient-dev -o dir::cache::archives="/home/runner/apt/cache"
-      sudo chown -R runner /home/runner/apt/cache
-  - name: Run tests
-    shell: bash
-    env:
-      RAILS_VERSION: ${{ inputs.rails-version }}
-      SOLIDUS_BRANCH: ${{ inputs.solidus-branch }}
-    run: |
-      bundle exec rake
-  - uses: actions/upload-artifact@v4
-    if: failure()
-    with:
-      name: Screenshots
-      path: |
-        spec/dummy/tmp/capybara
-        spec/dummy/tmp/screenshots
+    - uses: actions/checkout@v4
+    - name: Set up Ruby
+      uses: ruby/setup-ruby@v1
+      env:
+        DB: ${{ inputs.database == 'mariadb' && 'mysql' || inputs.database }}
+        DB_HOST: 127.0.0.1
+        DB_USERNAME: ${{ inputs.database == 'postgresql' && 'postgres' || 'root' }}
+        RAILS_VERSION: ${{ inputs.rails-version }}
+        SOLIDUS_BRANCH: ${{ inputs.solidus-branch }}
+      with:
+        ruby-version: ${{ inputs.ruby-version }}
+        bundler-cache: true
+        cache-version: ${{ inputs.rails-version }}-${{ inputs.solidus-branch }}-{{ inputs.database }}-{{ inputs.ruby-version }}
+        rubygems: "latest"
+    - name: Restore apt cache
+      id: apt-cache
+      uses: actions/cache@v4
+      with:
+        path: /home/runner/apt/cache
+        key: ${{ runner.os }}-apt-${{ inputs.database }}
+        restore-keys: |
+          ${{ runner.os }}-apt-
+    - name: Install libvips
+      shell: bash
+      run: |
+        mkdir -p /home/runner/apt/cache
+        sudo apt update -qq
+        sudo apt install -qq --fix-missing libvips -o dir::cache::archives="/home/runner/apt/cache"
+        sudo chown -R runner /home/runner/apt/cache
+    - name: Install Postgres headers
+      if: inputs.database == 'postgresql'
+      shell: bash
+      run: |
+        mkdir -p /home/runner/apt/cache
+        sudo apt update -qq
+        sudo apt install -qq --fix-missing libpq-dev -o dir::cache::archives="/home/runner/apt/cache"
+        sudo chown -R runner /home/runner/apt/cache
+    - name: Install MySQL/MariaDB headers
+      if: inputs.database == 'mysql' || inputs.database == 'mariadb'
+      shell: bash
+      run: |
+        mkdir -p /home/runner/apt/cache
+        sudo apt update -qq
+        sudo apt install -qq --fix-missing libmysqlclient-dev -o dir::cache::archives="/home/runner/apt/cache"
+        sudo chown -R runner /home/runner/apt/cache
+    - name: Run tests
+      shell: bash
+      env:
+        DB: ${{ inputs.database == 'mariadb' && 'mysql' || inputs.database }}
+        DB_HOST: 127.0.0.1
+        DB_USERNAME: ${{ inputs.database == 'postgresql' && 'postgres' || 'root' }}
+        RAILS_VERSION: ${{ inputs.rails-version }}
+        SOLIDUS_BRANCH: ${{ inputs.solidus-branch }}
+      run: |
+        bundle exec rake
+    - uses: actions/upload-artifact@v4
+      if: failure()
+      with:
+        name: Screenshots
+        path: |
+          spec/dummy/tmp/capybara
+          spec/dummy/tmp/screenshots