I think the best cover letter explains what you can do on day one, in three months, six months, and 1 year for the company that may potentially hire you.
Attach the cover letter as a separate document. If you can, get the email of the hiring manager and let them know that you've applied through the standard HR interface. Tone should always be professional and cordial. If you can craft this cover letter well enough you will stand out from others who don't customize their cover letters. Do your research on the company and find where your strengths can play to their business objectives and communicate why you are the one they should choose (then you can link to GitHub projects accordingly). Good luck.
Attach the cover letter as a separate document. If you can, get the email of the hiring manager and let them know that you've applied through the standard HR interface. Tone should always be professional and cordial. If you can craft this cover letter well enough you will stand out from others who don't customize their cover letters. Do your research on the company and find where your strengths can play to their business objectives and communicate why you are the one they should choose (then you can link to GitHub projects accordingly). Good luck.