Senior Web Developer

Castelion Corporation • Torrance, CA

3d

About The Position

Castelion is seeking a hands-on Senior Web Developer to lead the architecture, development, and production readiness of the Seeker Team’s internal web application. The application will bring together existing tools for calibration, field testing, machine-learning annotation and training, and Foxglove into a cohesive product for engineers and analysts.

The role is the technical owner of the application and works directly with end users to understand their workflows, make large-scale data accessible and responsive, and build reliable infrastructure that supports full-rate hardware manufacturing. The developer remains involved in implementation while setting technical direction, prioritizing work, and mentoring junior developers on a small team. The application should be ready to support full-rate hardware manufacturing by the end of 2027.

The position may require access to classified information or restricted U.S. Government sites, systems, or information. If designated, employment may depend on obtaining and maintaining required government clearance or authorization and meeting applicable citizenship or other eligibility requirements. The position also requires access to export-controlled information; hiring is contingent on the candidate’s ability to access applicable information without additional export licensing.

Requirements

• Experience leading a web application from architecture and implementation through production deployment.
• Strong proficiency in Python, FastAPI, and asynchronous programming with asyncio.
• Experience with PostgreSQL, object-relational mapping (ORM), and blob or object storage.
• Strong experience with a modern frontend framework and JavaScript or TypeScript, HTML, and CSS.
• Demonstrated ability to design responsive applications for large datasets and data-intensive workflows.
• Experience building reliable applications with automated testing, CI/CD, monitoring, and safe deployment and rollback strategies.
• Strong product judgment, user experience instincts, and ability to translate complex workflows into simple, effective software.
• Ability to mentor and delegate to junior developers while remaining hands-on.
• Demonstrated ownership of application quality, usability, reliability, and user adoption.
• Ability to access applicable export-controlled information without additional export licensing being required; government clearance or other authorization and eligibility requirements may apply if the position is designated.

Nice To Haves

• Experience with Plotly or similar data visualization libraries.
• Experience building internal engineering tools, scientific applications, or data-intensive web platforms.
• Familiarity with large-scale data discovery, visualization, and retrieval patterns.
• Experience integrating multiple tools or workflows into a unified application.
• Experience with background jobs, precomputation, streaming data, and performance optimization.
• Experience preparing applications for high-availability or production-critical environments.
• Ability to balance architectural decisions with near-term delivery in a small, fast-moving engineering team.

Responsibilities

• Lead the web application’s architecture and development from design through production, while remaining hands-on with implementation.
• Integrate calibration, field testing, ML annotation, ML training, and Foxglove into one application with clear navigation and consistent workflows.
• Work directly with engineers and analysts to understand needs, simplify workflows, and reduce manual steps and one-off scripts.
• Design data-fetching, caching, pagination, streaming, precomputation, background-processing, and visualization strategies for terabytes of data.
• Improve usability, adoption, responsiveness, and reliability so users can find tools and data without developer assistance.
• Establish reliable infrastructure, monitoring, automated testing, and safe deployment practices, including frequent releases and straightforward rollbacks.
• Prepare the application to support full-rate hardware manufacturing by the end of 2027.
• Set priorities, assign work, review designs and code, and mentor junior developers while contributing directly to development.
• Work within Castelion’s current technology stack where practical, making changes or replacements based on demonstrated results rather than personal preference.

What This Job Offers

• Job Type: Full-time
• Career Level: Senior
• Education Level: No Education Listed