Most software engineering jobs at large companies don't need a cover letter — the resume and the coding loop decide everything. But in three situations a short, specific letter genuinely moves the needle: applying to a small startup where a founder reads every word, switching careers or stacks where context isn't obvious from the resume, and supporting a referral so the person vouching for you has something concrete to forward. A good SWE cover letter is 150 to 250 words, names the specific role and one specific thing you'd work on, and shows you understand the company's technical problem. Skip it entirely at big companies with a portal and an automated loop.
When a cover letter actually matters
Be honest about the channel. If you're applying through a big company's portal into an automated loop, the letter is usually filed and never read — your effort is better spent tailoring the resume and preparing for the coding rounds. The cover letter earns its keep in three specific situations:
- Small startups. At a 10- or 30-person company, a founder or the first engineering hire often reads every application. A specific letter that shows you understand their problem is a real edge, because the team is hiring as much for judgment and fit as for raw skill.
- Career or stack switches. If your resume doesn't obviously map to the role — you're moving from data engineering to backend, from a different industry, or from a bootcamp into your first SWE job — the letter is where you supply the missing context in two sentences instead of leaving the reader to guess.
- Referrals. When someone refers you, a short letter gives them something concrete to forward and gives the hiring manager a reason to prioritize the intro. Here the letter does the explaining so your referrer doesn't have to.
A real example, broken down
Here's a 190-word letter for a backend role at a Series A startup, written by an engineer with a few years of relevant experience. Read it first, then the breakdown.
Hi Dana,
I'm applying for the Backend Engineer role. I've been following Cobalt since your post on moving billing off a monolith — I spent the last two years doing exactly that migration at Lumen, so the problem you described is one I've actually lived.
At Lumen I led the extraction of our payments service out of a Rails monolith into a Go service behind gRPC, handling idempotency and partial-failure retries that had previously caused double-charges. It cut billing-related incidents from roughly one a month to zero over the following two quarters and let the team deploy payments independently. Your stack (Go, Postgres, Temporal) lines up closely with what I ran in production there.
I'd be glad to walk through how I'd approach the migration ordering for your billing cutover. Thanks for reading.
— Sam Ortiz
What makes it work, paragraph by paragraph:
- Opening: names the role and one specific, verifiable thing about the company (a public post about a real technical problem). This is the line that proves you didn't mass-mail.
- Middle: one concrete piece of relevant work — a real migration — with a measurable result (incidents from ~1/month to zero) and the stack named as evidence, not as a keyword list.
- Close: a single forward-looking line offering something specific (how he'd sequence their cutover), then out. No "I'd be a great fit," no restating the resume.
Fix the opening line
The first sentence does most of the work. A generic opener tells the reader you sent the same letter to fifty companies; a specific one tells them you understand their actual problem. Same candidate, two openings:
I am writing to express my strong interest in the Software Engineer position at your company. I am a passionate and results-driven engineer looking for a challenging new opportunity.
I'm applying for the Backend Engineer role. I spent the last two years extracting a billing service out of a Rails monolith — the exact migration your engineering post described — and would love to help with yours.
Drops the boilerplate; names the role and a specific, relevant thing you can do for them.
With a solid background in various programming languages and frameworks, I am confident I would be a valuable addition to your dynamic team.
I ran a Go and Kafka event pipeline at ~40k events/sec in production for two years — the same scale and stack your job description mentions — so the throughput problems you listed are familiar territory.
Replaces vague confidence with a concrete claim tied to their stated stack and scale.
What to cut
Most weak SWE cover letters are padded with the same filler. Cut all of it:
- "I am passionate / results-driven / detail-oriented." Adjectives about yourself prove nothing. A metric does the proving for you.
- A restatement of your resume. The reader has the resume. The letter adds context or judgment the resume can't, or it adds nothing.
- A list of technologies. That's the resume's job. In the letter, the stack appears once, inside a concrete claim.
- "Thank you for considering my application" as a paragraph. A one-line close is enough; a paragraph of gratitude reads as filler.
The honest summary
For most software engineers, the cover letter is optional — skip it at large companies with an automated loop. When a human will read it (startups, switches, referrals), write 150 to 250 words: one specific reason you're applying here, one concrete piece of relevant work with a result, and a one-line close. Name the stack only as evidence, cut every adjective about yourself, and never reuse a generic draft. For broader context on the role and demand, the BLS Occupational Outlook for software developers is a reliable reference. A sharp, specific letter is a small edge in the few cases it's read — and a waste of effort everywhere else.
Common questions
- Do software engineers even need cover letters anymore?
- Usually not. At large companies, the resume and the coding/system-design loop carry the decision, and many portals don't surface the letter to anyone. Write one when a human will actually read it: small startups, career or stack switches that need context, and referral introductions. When in doubt at a big company, skip it and put the energy into tailoring the resume.
- How long should a software engineer cover letter be?
- 150 to 250 words. Three short paragraphs: why this company specifically, one concrete piece of relevant work with a result, and a one-line close. Anything longer and a busy founder or hiring manager stops reading. The goal is a sharp, specific signal, not a complete narrative of your career.
- Should I mention the specific tech stack in my cover letter?
- Yes, briefly and only where it's true. Naming that you've run their exact stack in production — "scaled a Go and Kafka pipeline to similar volume" — is a strong, specific signal. Don't list technologies for keyword stuffing; that's the resume's job. In the letter, the stack should appear as evidence inside a concrete claim.
- Can I reuse one cover letter for every application?
- No. A generic letter is worse than none — it signals you didn't look closely, which is the opposite of what a small team wants. You can reuse a skeleton, but the opening line and the one concrete example must be specific to each company and role. If you can't name something specific about them, that role probably doesn't warrant a letter.
Sources
Keep reading
Do cover letters still matter in 2026?
Cover letters still matter in specific situations. When recruiters actually read them by company size and role type, the real ROI, and where to spend effort.
How long should a cover letter be?
A cover letter should run 150 to 300 words across three or four short paragraphs. Why shorter wins, and the hook-fit-close structure that fits the length.
Is it OK to use AI to write my cover letter?
Using AI to draft a cover letter is fine with discipline: AI handles structure, you supply specifics and voice. The slop tells recruiters notice, and how to kill them.
Product manager cover letter examples
When a product manager cover letter is worth writing, plus a real 200-word example that ties product wins with metrics to the company's specific problem.