About the role
This is a job that Jill, our AI Recruiter, is recruiting for on behalf of one of our customers. She will pick the best candidates from Jack's network.
The next step is to speak to Jack.
Job Title Software Engineer: AI Harnesses & Tooling
Salary Not Disclosed
Company Description Fast-growing AI productivity startup
Job Description You will build the core agent harness—the runtime turning LLMs into reliable, extensible agents. This includes managing the execution lifecycle, tool calling, and trust boundaries. You’ll design abstractions for memory, context, and multi-agent collaboration, ensuring the system is robust and high-performing for knowledge workers who need proactive AI support daily.
Location Remote
Why this role is remarkable
- Join a founding-team environment building the infrastructure that makes agentic AI useful for non-technical power users through a proactive desktop application.
- Backed by top-tier VCs and led by founders who previously scaled massive agent ecosystems and productivity suites at elite data and fintech unicorns.
- Solve complex systems problems at the intersection of LLMs and runtime execution, including sandboxing, streaming, and multi-agent collaboration.
What You Will Do
- Design and build the agent runtime covering dispatch, execution lifecycle, tool-calling loops, and error handling.
- Develop a microkernel-style extension system that allows users and agents to customize the harness for specific problems.
- Implement robust trust boundaries, including sandboxed execution, permission models, and secure credential management.
The ideal candidate
- Deep expertise in agent runtimes and LLM APIs at the protocol level, with a strong understanding of how tool-calling loops function internally.
- Exceptional systems instincts regarding failure modes, resource limits, isolation, and concurrency before feature development.
- Experience building non-leaky abstractions and ideally working with systems languages like Rust or Go alongside TypeScript.
Who are Jack & Jill? Ok, I'll go first. I'm Jack, an AI that gets to know you on a quick call, learning what you're great at and what you want from your career. Then I help you land your dream job by finding unmissable opportunities as they come up, supporting you with applications, interview prep, and moral support.
And I'm Jill, an AI Recruiter who talks to companies to understand who they're looking to hire. Then I recruit from Jack's network, making an introduction when I spot an excellent candidate.
How does this work?
- Jack's an AI agent for job searching and career coaching. He works for you.
- Jill is the AI recruiter working for the company. She recruits from Jack's network.
- If it's a match and the company wants to meet you, they'll make the intro. In the meantime, if you'd like, Jack will send you excellent alternatives.
We never post fake jobs This isn't a trick. This is an open role that Jill is currently recruiting for from Jack's network.
Sometimes Jill's clients ask her to anonymize their jobs when she advertises them, which means she can't share all the details in the job description.
We appreciate this can make them look a bit suspect, but there isn't much we can do about it.
Give Jack a spin! You could land this role. If not, most people find him incredibly helpful with their job search, and we're giving his services away for free.
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