Junior Software Engineer

Ultrasonium; Woburn (MA); On-site; USD 120,000 - 180,000; Full time

Benefits offered by this job

Stock options or equity

Direct mentorship from founding team

Ownership of real services

Lean on-site environment

Job summary

Ultrasonium is seeking a versatile software engineer to build and maintain full-stack features, primarily with Next.js and Python APIs, while supporting embedded firmware and collaborating with electrical, controls, mechanical and process teams.

You will work directly with the founding team from implementation to working deployment, documenting learnings and ensuring service reliability and scalability in a lean on-site environment.

Qualifications

• Bachelor's degree or equivalent project experience in CS or related field.
• Hands-on full-stack web development with deployed projects.
• Experience with Next.js and Python, building or consuming HTTP APIs.
• Familiarity with Git, Linux, and deploying services to cloud/server env.

Responsibilities

• Build and maintain full-stack web features, primarily in Next.js.
• Develop Python APIs with FastAPI and MCP servers with FastMCP.
• Provision and operate deployment environments and health checks.
• Support embedded firmware interfacing with sensors and hardware teams.
• Document learnings and keep internal tools and runbooks current.
• Write tests and ensure reliability of services after deployment.

Skills

Full-stack development

Next.js experience

Python

HTTP APIs

Git & Linux

Education

Bachelor's degree in CS or related

Tools

Docker

CI/CD

Cloud deployment

Job description

You will work across full-stack web development and the systems that run our services. That includes Next.js applications, Python APIs with FastAPI, MCP servers with FastMCP, and the provisioning and deployment work that keeps those services available. You will also support embedded firmware and take on software tasks that help the electrical, controls, mechanical, and process teams. You will work directly with the founding team and take features from implementation through a working deployment.

You might be a great fit if you...

• You like shipping a feature and then making the service that runs it reliable.
• You can move between a web interface, an API, and the system that hosts it.
• You are willing to support firmware and other tasks that sit between software and the hardware teams.
• You document what you learn and ask for help when you are stuck.
• You communicate clearly with engineers outside software.

Key responsibilities

• Build and maintain full-stack web features, primarily in Next.js.
• Develop Python API services with FastAPI and MCP servers with FastMCP.
• Provision and operate the environments those services depend on, including deployment configuration and basic service health checks.
• Support embedded firmware for the electrical and controls teams, including interfaces to sensors, actuators, and motion hardware.
• Help electrical, controls, mechanical, and process engineering with software tasks that unblock their work.
• Write tests for the features and services you own.
• Keep internal tools, service documentation, and runbooks current.
• Support internal software for physical AI process control, which is in development.

Required qualifications

• Bachelor's degree in Computer Science, Software Engineering, or a related field, or equivalent project experience.
• Hands-on full-stack web development experience, including a deployed project, internship, or equivalent work.
• Experience with Next.js or a comparable React framework, and with Python.
• Experience building or consuming HTTP APIs.
• Familiarity with Git, Linux, and deploying a service to a cloud or server environment.

Preferred qualifications

• Experience with FastAPI, FastMCP, or another MCP server.
• DevOps or provisioning experience with Docker, infrastructure-as-code, CI, or Cloudflare Workers.
• Experience operating a small production service, including logs, environment configuration, and follow-up after a failure.
• Coursework or project experience with embedded firmware, microcontrollers, or C/C++.
• Interest in software for manufacturing or hardware systems.

What we offer

• Y Combinator and NSF-backed startup.
• Stock options or equity.
• Direct mentorship from the founding team, with ownership of real services.
• Direct collaboration with the founding team on a process with no direct commercial equivalent.
• A lean, on-site environment where your technical judgment shapes product direction.
• The opportunity to file patents and contribute to a growing IP portfolio.
• Flexible working arrangements and a culture that respects your time and autonomy.