Do you need one?

Send one when the application asks for it, when there's something the resume can't explain (a career change, a move, a gap, a referral), or when you really want the role. When it's marked optional, a short, specific letter still helps more often than it hurts. A generic one doesn't.

Structure

Greeting
The hiring manager's name if you can find it; otherwise “Dear hiring team”. Avoid “To whom it may concern”.
Opening (2–3 sentences)
The role you're applying for and the most compelling reason you fit, stated plainly. Mention a referral here if you have one.
Evidence (1–2 paragraphs)
Two or three examples that match the posting's main requirements, with results. Pick different examples from the top of your resume, or tell the story behind one.
Why them (1 paragraph)
Something specific about the company, product, team or mission that connects to your experience. This is the part generated or copied letters get wrong.
Close (1–2 sentences)
Say you'd welcome a conversation and thank them. Sign off with your name.

A full example

Dear Ms Rao,

I'm applying for the Operations Analyst role at Harbourline Logistics. For the past three years I've built the reporting that a 120-person warehouse team uses to plan shifts, and I'd like to bring that work to a company running routing at Harbourline's scale.

At Eastgate Supplies, I replaced a set of spreadsheets with a SQL and Power BI dashboard that showed pick rates by hour. Supervisors used it to move staff between zones during peaks, and late dispatches fell from 9% to 4% over two quarters. I also led the rollout of barcode scanning in returns, which cut average processing time from two days to under one.

Your posting mentions the move to same-day delivery in three new cities. Forecasting demand for a service before there's history to rely on is exactly the problem I've enjoyed most, and I've done a smaller version of it when we opened our second site.

I'd welcome the chance to talk about how I could help. Thank you for your time.

Kind regards,
Arjun Mehta

Fictional names and companies. About 200 words.

Tone and length

Under one page: 250–400 words, three or four paragraphs. Write the way you'd speak in a good interview: clear, direct, specific. Match the company's register (a startup and a law firm read differently), but always stay professional. Use “I” naturally here; it's a letter.

Mistakes that get letters skipped

  • Opening with “My name is…” or “I am writing to apply for…” and nothing else.
  • Repeating the resume bullet by bullet.
  • Focusing on what the job would do for you rather than what you'd bring.
  • A “why this company” paragraph that could name any company.
  • The wrong company name, left over from another application.
  • Claims that aren't on the resume and can't be backed up.

Checklist

  • Addressed to a person or the hiring team, with the right company name.
  • The first two sentences say which role and why you fit.
  • Two or three examples with results, matched to the posting.
  • One paragraph specific to this employer.
  • Under one page, read aloud once for tone.
  • Every claim matches your resume.