Senior Software Engineer, Full Stack

AtoB Inc.; San Francisco (CA); On-site; USD 120,000 - 160,000; Full time

Job summary

AtoB Inc. is seeking a skilled engineer in San Francisco to lead technical projects and design robust APIs for our innovative products.

The ideal candidate has over 5 years of experience in B2B or B2C SaaS, thrives in a high-ownership environment, and is adept at balancing speed with rigorous documentation.

This role requires in-office work 4 days per week in either the San Francisco Bay Area or New York.

Qualifications

• 5+ years of professional experience in building SaaS products.
• Strong ability to work in zero-bureaucracy, high-ownership environments.
• Experience in balancing speed with rigorous testing and documentation.

Responsibilities

• Lead ambiguous technical projects to evolve and scale early-stage products.
• Design and maintain user-facing APIs and systems.
• Work end-to-end on frontend and backend projects.

Skills

Building B2B or B2C SaaS products

Experience in FinTech

Ability to communicate across time zones

React

Ruby

Postgres

Job description

Responsibilities

• Lead efforts for often ambiguous technical projects, laying the groundwork for early-stage products to iteratively evolve and scale.
• Design, build, and maintain APIs, user-facing experiences, services, and systems.
• Make effective tradeoffs between business priorities, user experience, and reliability.
• Work with critical frontend, backend & platform projects end-to-end—from design to production ops.
• Push architecture that scales to billions in annual payment volume and real-time risk controls.
• Work closely with product and GTM leads to turn ambiguous problems into elegant code.

Qualifications

• Have 5+ years of professional experience building B2B or B2C SaaS products (FinTech, payments, or marketplace a plus).
• Thriving in zero-bureaucracy, high-ownership environments.
• Balance speed with rigor—automated tests, clean abstractions, clear docs.
• Can participate in architecture discussions and still dive deep into code (we use React, Ruby, Postgres but great engineers pick up tools fast).
• Communicate crisply across time zones.
• This role is required to be in office 4 days/week (Mon-Thurs) either in San Francisco Bay Area or New York.