Founding Full Stack Engineer (Frontend + UX Focus) (San Francisco)HartleyCo • San Francisco, CA, US

Founding Full Stack Engineer (Frontend + UX Focus) (San Francisco)

HartleyCo • San Francisco, CA, US

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Founding Full Stack Engineer (Frontend + UX Focus)

Location : San Francisco (on-site)

Were helping a YC-backed, seed-stage startup hire a Founding Engineer who can take full ownership of the products look, feel, and overall experience. The company builds the simulation and evaluation layer for voice and text AI agents, used by both fast-growing startups and large enterprises.

This role is full stack, but the centre of gravity is very much the frontend. Youll be the person who makes a complex AI platform feel simple, fast, and genuinely enjoyable to use.

What Youll Own

End-to-end ownership of core UI : dashboards, debugging tools, evaluation workflows.
Turning rough ideas into product : sketching, prototyping and shipping quickly.
Driving UX quality across the product : layout, interaction, states, polish.
Building intuitive interfaces over real-time systems, large datasets, and AI outputs.
Dipping into the backend (Python / FastAPI, Supabase, AWS) to unblock yourself and shape APIs.

What Theyre Looking For

Strong front end engineering with sharp product taste.

Someone who cares about clean UI, clear UX flows, and fast interactions.

Ability to work full stack when needed, but happiest owning the product surface.

Comfortable working on-site with founders, shipping quickly, and iterating with customers.

Opinionated about design details and code quality.

Nice-to-Haves

Experience with React, TypeScript, Next.js, Tailwind.

Exposure to AI / voice tooling a bonus, not required.

Prior early-stage or YC / VC-backed startup experience.

Examples of beautiful or highly polished UI youve built.

If you want to define the visual and interactive identity of a high-velocity AI product and sit at the heart of a tiny founding team, this is the one.

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