A Senior Software Engineer cover letter that gets read.

Dear Hiring Manager, When I led the migration of [Company]'s monolithic payment service to microservices, reducing API response times by [specific percentage] and cutting infrastructure costs by [amount], I learned that technical decisions compound. Over [X years], I've built systems handling [scale metric like "10M+ daily transactions"] while mentoring [number] junior engineers through code reviews and architectural discussions. My work on [specific system/project] taught me that scalability isn't just about throughput—it's about making systems others can confidently modify and extend. At [Current/Previous Company], I own full lifecycle responsibility for [service area]—from design documents and database schema decisions through production monitoring and incident response. I've optimized [specific component], implemented [relevant technology/pattern], and established observability practices that reduced MTTR by [metric]. I'm equally comfortable diving into distributed systems challenges and refactoring legacy codebases; both require clear thinking about tradeoffs and communication with stakeholders. I'm drawn to [Company] because of [specific technical initiative, architecture choice, or engineering challenge]. Your [particular product/system] approach aligns with how I think about [relevant principle], and I'm excited to contribute to problems at that scale. I'd welcome discussing how my experience with [relevant skill] and track record of [specific achievement] can help your team.