A cover letter is not a formality you fill in to look polite. It is a short argument: here is why I am a sensible person to interview for this specific job. The format exists to make that argument fast, because the person reading it has thirty other letters to get through.
Get the structure right and the writing gets easier, because each paragraph knows what it is for. Get it wrong and you end up with a wall of text that restates your CV in full sentences. Nobody wants to read that, including the recruiter.
What the page should look like
Before the words, the layout. A cover letter should fit on one page, no exceptions. Use the same font as your CV so the application looks like one document. Standard margins, left-aligned text, a clear line between paragraphs.
At the top, your name and contact details, then the date, then the company details if you have a named contact. A subject line stating the role helps a busy reader file it correctly. If you are sending the letter as an email rather than an attachment, the email body is the letter; do not write "please see attached" and leave the body empty.
The four paragraphs
Most effective cover letters are four paragraphs. Not three, not seven. Four.
Paragraph one: why you are writing. Name the role and where you saw it. Then add one sentence that is not generic, a reason you are interested that shows you know something specific about the company or the work. Skip "I am writing to apply for." The reader already knows that from the subject line.
Paragraph two: your strongest relevant proof. Pick the one achievement that maps most directly to what the job needs. Tell it as a short story: the situation, what you did, the result. One concrete example beats three vague claims. This is the paragraph that earns the interview.
Paragraph three: why this company. Connect your goals to theirs. This is where research shows. A line about a product they shipped, a value they act on, a problem you know they are working on. If this paragraph could be sent to any company in the industry, rewrite it.
Paragraph four: a clean close. Thank them, state that you would welcome the chance to talk, and stop. No begging, no listing your availability across three time zones. One or two sentences.
Length and tone
Aim for 250 to 400 words total. Shorter is usually better than longer. If you are past 400, you are probably restating the CV.
The tone is professional but human. Write the way you would speak in a first interview: clear, warm, confident without overselling. Contractions are fine. Long, formal constructions like "I would hereby like to express my keen interest" make you sound like a template.
Mistakes that get a letter skimmed
- Opening with your life story. The reader wants the role and the reason, fast. History goes in the CV.
- Restating the CV in prose. The cover letter adds context the bullet points cannot, not the same facts in longer form.
- Addressing it "To whom it may concern." Find a name. If you genuinely cannot, "Dear Hiring Manager" is acceptable; the older phrasing reads as a mass mailing.
- One letter for every application. A recruiter spots a generic letter immediately. Paragraphs one and three have to change for each company.
- Typos in the company name. It happens when you reuse a letter and miss a find-and-replace. It also ends the application.
Tailor the variable parts
Paragraphs two, three, and the specific sentence in paragraph one change with every application. The skeleton stays. That is the point of having a format: the structure is reusable, the content is not.
If your CV is built from a LinkedIn profile with a tool like Postulit, you already have your achievements written out in one place, which makes choosing the right proof for paragraph two much faster.
Write the letter after you have read the job posting twice. The second read is where you notice what they actually care about, and that is the letter's whole job to address.