Software Engineer - Backend

Koah; San Francisco (CA); On-site; USD 80,000 - 120,000; Full time

Job summary

A growing tech startup in San Francisco is seeking candidates passionate about building AI-native products in the ad tech space. Ideal candidates should have a strong background in performance optimization and software development, particularly with technologies such as Ruby on Rails and React. Join a small, fast-paced team that values creativity, trust, and the craft of coding while contributing to innovative projects shaping the ad ecosystem.

Qualifications

• Experience with debugging and optimizing performance in software applications.
• Attention to detail with a track record of creating reliable abstractions.
• Interest in experimentation and performance measurement.

Responsibilities

• Build scalable data models for ad requests.
• Design systems for new ad formats and engagement tracking.
• Develop low-latency frequency capping systems.

Skills

Debugging and performance optimization

Detail-oriented

Experimentation and measuring

Tools

Ruby on Rails

React

TypeScript

PostgreSQL

AWS

Job description

Who We Are

Koah Labs is building the ad network to power the next generation of AI-native products. Our mission is to help publishers monetize and help advertisers reach the right audience — without compromising speed, UX, or privacy.

We’re a small, tight-knit team in San Francisco with backgrounds at X, Apple, Meta and early-stage startups. We’ve raised from top investors and are growing fast with real traction on both the publisher and advertiser sides of the marketplace.

Working at Koah means joining at the ground floor: you’ll ship code that shapes the company and the ecosystem we’re building. We move quickly, operate with high trust, and care deeply about craft.

Our Stack

• Infra: Terraform, AWS, LGTM (Loki, Grafana, Tempo, Mimir), Tailscale, Cloudflare
• Data: PostgreSQL, ClickHouse, Redis, Kafka, Python
• Core Application: Ruby on Rails, React, TypeScript
• SDKs: Flutter, React Native, Android, iOS

Example projects

• Build scalable data models that support multiple impressions for an ad request
• Design abstractions that allow us to experiment and ship new formats that allow for a flexible way of tracking engagement events
• Build a low-latency frequency capping system to improve an end user\'s experience

You might be a fit if

• You like debugging and optimizing performance
• You are detail oriented and like to create good abstractions that others rely on
• You enjoy experimentation, measuring, and creating reliable systems