diff --git a/.github/workflows/test.yml b/.github/workflows/test.yml
new file mode 100644
index 0000000..ffe3662
--- /dev/null
+++ b/.github/workflows/test.yml
@@ -0,0 +1,19 @@
+name: Tests
+
+on:
+  pull_request:
+    types: [opened, reopened, synchronize]
+    branches:
+      - main
+
+jobs:
+  test:
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/checkout@v4
+    - uses: ruby/setup-ruby@v1
+      with:
+        ruby-version: '3.3'
+    - run: ruby main.rb
+      env:
+        FILENAME: test.txt
diff --git a/README.md b/README.md
index 6e7b125..77394ad 100644
--- a/README.md
+++ b/README.md
@@ -1,2 +1,6 @@
 # version-check
-Checks if version is upgraded when updating the repository
+Checks if version is upgraded when updating the repository. Pass regex for version strings and a filename to test if it has been updated.
+
+## Set version format regex
+
+I use ruby regex (rubular) for the version strings. The default value is `/[v]\d.\d.\d/` (which means e.g. v1.0.0). You can test your own formats at: https://rubular.com/.
diff --git a/action.yml b/action.yml
new file mode 100644
index 0000000..6ec865a
--- /dev/null
+++ b/action.yml
@@ -0,0 +1,25 @@
+name: "version-checker"
+description: "Checks if you updated the version in your code."
+inputs:
+  filename:
+    description: "Filename that contains the version."
+    required: true
+  version-regex:
+    description: "Ruby regex of the versions (e.g. /[v]\d.\d for v1.0)"
+    required: false
+    default: "/[v]\d.\d.\d/"
+
+branding:
+  icon: "package"
+  color: "red"
+runs:
+  using: "composite"
+  steps:
+    - uses: actions/checkout@v4
+    - uses: ruby/setup-ruby@v1
+      with:
+        ruby-version: '3.3'
+    - run: ruby main.rb
+      env:
+        VERSION_REGEX: ${{ inputs.version-regex }}
+        FILENAME: ${{ inputs.filename }}
diff --git a/main.rb b/main.rb
new file mode 100644
index 0000000..c9db91e
--- /dev/null
+++ b/main.rb
@@ -0,0 +1,53 @@
+#!/usr/bin/ruby
+
+class Project
+
+    attr_reader :code_tags, :git_tags
+
+    def initialize(filename, version_regex)
+        # variables
+        @filename = filename
+        @version_regex = version_regex
+        # upon init
+        @code_tags = []
+        @git_tags = []
+        read_versions
+        get_tags
+    end
+
+    def read_versions()
+        File.open(@filename, "r") do |f|
+            f.each_line do |line|
+                @code_tags += line.scan(@version_regex)
+            end
+        end
+    end
+
+    def get_tags()
+        @git_tags = Dir.entries(".git/refs/tags/").select{ |i| i[@version_regex] }
+    end
+
+    def version_updated()
+        for code_tag in @code_tags do
+            if not @git_tags.include? code_tag
+                return true
+            end
+        end
+        return false
+    end
+
+end
+
+begin
+    regex = ENV["VERSION_REGEX"]  || "/[v]\\d.\\d.\\d/"
+    filename = ENV["FILENAME"] || ""
+
+    if filename.empty?
+        raise "No filename passed as env."
+    end
+
+    project = Project.new(filename, eval(regex))
+    if not project.version_updated
+        raise "Version in code not updated."
+    end
+end
\ No newline at end of file
diff --git a/test.txt b/test.txt
new file mode 100644
index 0000000..5b213d6
--- /dev/null
+++ b/test.txt
@@ -0,0 +1,10 @@
+something
+something
+something
+something
+version=v1.0.0
+something
+else
+
+
+version=v1.0.1