Senior Staff Engineer, Tax Platform Engineering

StartupXO; San Francisco, Northern (CA, KY); Hybrid; USD 223,000 - 278,000; Full time

Benefits offered by this job

Equity

Job summary

StartupXO in San Francisco is seeking a Backend Staff engineer who owns the payroll platform that calculates, pays and files taxes for more than 500,000 US small businesses. The role scales a large Ruby on Rails and TypeScript React codebase while delivering guardrails for agentic AI in tax concepts.

You set the technical strategy and roadmap for your domain and lead legacy overhauls across several teams, reflecting ten-plus years of senior Rails and React experience.

Qualifications

• 10+ years of senior Rails/React experience.
• Experience owning large Rails/React services at scale.
• Payroll tax domain knowledge is a plus.

Responsibilities

• Own the payroll platform for 500,000+ US small businesses.
• Lead large overhauls across multiple teams and set technical strategy.
• Build guardrails so agentic AI can touch tax concepts safely and accurately.

Skills

Ruby on Rails

TypeScript React

Leadership

Payroll tax knowledge

Job description

Backend Staff Hybrid 10yr+ Denver, San Francisco, New York, Chicago, US (2 to 3 office days a week)

You own the platform that calculates, pays and files payroll taxes for more than 500,000 US small businesses. The job scales one of the largest Ruby on Rails and TypeScript React codebases anywhere while building guardrails so agentic AI can touch tax concepts without compromising accuracy or compliance. You set the technical strategy and roadmap for your domain and lead legacy overhauls across several teams, which is why the posting asks for ten-plus years; base pay is $223,000 to $278,000 in San Francisco with equity on top.

Why this role fits

Payroll tax is a domain where a mistake turns into a penalty right away, so accuracy comes before speed. It suits someone who likes systems where change is deliberate and the blast radius is wide, and who has run large Rails and React services for years. Payroll, tax or compliance experience is preferred, not required.