Senior Full Stack Engineer

Sincere is looking for a Senior Full Stack Engineer to help us make our products meaningfully better. This is a high-ownership individual contributor role for a seasoned engineer who can take a broad product area, understand the customer and business needs, and turn those insights into polished, user-facing improvements.

Our primary application stack is Ruby on Rails and Next.js. We're open to engineers with strong full-stack experience in Rails or closely related backend frameworks such as Django/Python, Laravel/PHP, or Phoenix/Elixir. We're looking for engineers with deep React and Next.js experience and a strong track record of owning customer-facing product work across the full stack.

You will:

• Build and ship full-stack product features across Ruby on Rails and Next.js
• Own product initiatives end-to-end, from identifying opportunities and shaping solutions through implementation, launch, measurement, and iteration
• Build user-facing features and experiences that make our products more useful, intuitive, and enjoyable
• Partner closely with product/project managers and designers to understand customer pain points, evaluate opportunities, and determine what should be built
• Use Claude Code and Codex as a core part of your development workflow to explore codebases, develop solutions, test ideas, and ship efficiently
• Make practical technical decisions that balance speed, quality, maintainability, performance, and customer impact
• Work across the frontend and backend as needed, rather than being limited to one layer of the stack
• Use tools like Datadog and Mixpanel to understand production behavior, investigate issues, measure impact, and inform product decisions
• Champion new ideas and continuously look for ways to improve our products, engineering practices, and customer experience

You are:

• A seasoned full-stack engineer with 7+ years of professional software development experience
• Highly experienced with React and Next.js and comfortable owning customer-facing experiences from frontend through backend
• Experienced with Ruby on Rails or a closely related product-focused backend framework such as Django/Python, Laravel/PHP, or Phoenix/Elixir
• Fluent with AI-assisted development tools such as Claude Code or Codex and already use them meaningfully as part of your software development workflow
• Proven at building, launching, and improving large-scale customer-facing web applications
• Able to point to meaningful user-facing or visual product improvements you've helped shape and ship, not just improvements to the underlying code or architecture
• Product-minded, with strong instincts for customer needs, UX quality, business value, and technical tradeoffs
• A self-starter who brings structure to loosely defined problems and drives them through execution
• Comfortable working in a modern production environment that includes TypeScript, MySQL/Postgres, Redis, MongoDB, Sidekiq, OpenSearch, AWS, Docker, and related infrastructure
• A strong partner to DevOps, with enough understanding of system architecture, cloud infrastructure, deployment, containerization, and infrastructure-as-code to collaborate effectively
• Skilled at working in mature codebases, understanding existing architecture, and improving systems pragmatically
• Detail-oriented, with high standards for both the code and the customer experience
• Entrepreneurial, curious, and biased toward building, experimenting, and shipping
• Collaborative and low-ego, with strong communication skills and pride in your craft