A cover letter’s purpose is to quickly introduce you, your skills, why you feel you are the best candidate for the position, and extend your invitation for a face-to-face interview (or video conferencing). It completes the resume and application package, and generally the expectation, unless otherwise stated, is that a tailored one should be written for each job you apply to.
When writing a letter, you should go to the company’s website to understand their corporate culture and apply some of the details to the letter. Showing that you have done your homework by outlining why you would be the best fit for their team, can go a long way in convincing a hiring manager to call you.
The most important part of cover letter writing is specificity. Each cover letter should recap your experience to highlight specific criteria of the job posting or description that you are well equipped to perform. Keep it short and to the point, and change it for every job that you apply to. Yes, you read that correctly! Rewrite it for each job posting. Having a universal cover letter is better than having no letter at all, but not as good as a specifically crafted letter.