My usual cover letter:

Dear Sir/Madam, in reply for Your job offer placed at <website> I would like to apply for a <position>.

I'm <someone> with <x> years of experience. I <do stuff> and <do other stuff>.

My current tech-stack is: <my tech stack>

I've included my CV as an attachment for this message.

Looking forward for a reply from You.

Best regards,

<me>

Enjoy ;)