Harness Engineer

Virio; San Francisco (CA); On-site; USD 150,000 - 250,000; Full time

Benefits offered by this job

Founders exposure

Equity upside

Medical, dental, and vision insurance

401(k) plan

Meals provided

Relocation support to San Francisco

Annual off-site

Career progression

In-person culture

Job summary

Virio is seeking a Harness Engineer in San Francisco to own the intelligence layer between our AI models and the product, including system prompts, tool definitions, context management, and evaluation framework.

You'll design evaluation methods, architect multi-step workflows, and drive prompt versioning and improvements with cross-functional teams to ship impactful AI capabilities.

Qualifications

• Experience building prompts, evaluation frameworks, or harnesses for AI systems.
• Nice to have background in English, literature, creative writing, or humanities.

Responsibilities

• Own the intelligence layer between AI models and product, including system prompts, tool definitions, context management, and evaluation framework.
• Design the evaluation framework to ship with confidence and define success metrics.
• Architect the abstraction layer between product assets and model capabilities for reliable multi-step workflows.
• Own prompt versioning, experimentation, and iteration with A/B testing of prompts.
• Collaborate with product and engineering to identify signal and translate into prompt and architecture improvements.

Job description

Harness Engineer

Location: San Francisco (in-person, in-office, full-time ONLY)

Compensation: $150k-$250k base + top of market equity

About Virio

Virio is solving an unsolved problem: how do you write perfect content? The best human strategist researches the space, finds the angle, and knows your goals and constraints — but they're capped by the hours in a day and one human career's worth of expertise. An agent isn't.

Crafting "perfect" content has three components:

1. Research: to identify and collect the best inputs

2. Synthesis: to devise the strategy and execute on it

3. Verification: RL verification of content quality and efficacy

We're backed by operators from LinkedIn, YouTube, HubSpot, Rippling, and Google. The team is almost 100% ex-founders and VCs from Yale, UC Berkeley, Stripe, and more. And we've consecutively added $1M ARR/mo because everyone and their co-founder wants what we're selling.

This problem doesn't have a playbook. We're looking for a Harness Engineer to obsess over AI-for-writing and own that layer end to end: the data feedback loop, evals, and harness design that turn a subjective judgment into something we can measure and improve — so day by day, we can get ever closer to solving content.

What You'll Do

As a Harness Engineer, you'll own the intelligence layer that sits between our AI models and product—the system prompts, tool definitions, context management, and evaluation framework that makes agents actually work in production.

Specifically:

• Build and refine the system prompts, tool integrations, and context windows that shape how our models behave across our platform—you'll see how small prompt tweaks cascade into measurable product impact. (Nice to have: background in English, literature, creative writing, or humanities)

• Design the evaluation framework (LLM-as-judge evals, deterministic tests, production monitoring) that lets us ship with confidence. You'll define what success looks like and build the metrics to measure it.

• Architect the abstraction layer between our product (file systems, artifacts, skills) and the model's capabilities—making complex multi-step workflows feel natural to the model and reliable to users.

• Own prompt versioning, experimentation, and iteration. You'll A/B test prompt variations, measure their impact on agent quality, and ship improvements across our production system.

• Collaborate with product and engineering to identify signal—where our agents are failing, where users are stuck—and translate that into prompt and architecture improvements.

What Success Looks Like

• After 30 days: You understand our agent stack—the system prompts, available tools, context window strategy, and current failure modes. You've shipped your first prompt improvement and measured its impact.

• After 90 days: You've designed and implemented our core evaluation framework. Our team uses it as the source of truth for agent quality. You've shipped 2-3 meaningful prompt iterations that improved measurable outputs, and you're comfortable making architecture trade-offs.

• After 6 months: You own the harness layer end-to-end. You've architected improvements that reduced hallucination, improved context retention, or increased model reliability. You're driving architectural decisions about how we expose capabilities to the product team. You're writing technical content about how we've solved these problems—attracting the next generation of harness engineers to the company.

Traits That Thrive at Virio

• High agency & self-direction – Acts without waiting for requirements or detailed instructions

• Small-team intensity comfort – Comfortable working intensely and closely with a small, high-output team

• Unorthodox problem solving – Sees non-obvious paths forward and challenges conventional approaches

• Quality-driven execution – Detail-oriented with high standards for correctness and quality

• Low ego & accountability – Takes full ownership and accountability for outcomes

Benefits

• Work directly with the founders

• Competitive total compensation aligned to impact and ownership

• Meaningful equity upside as part of the founding team

• Medical, dental, and vision insurance

• 401(k) plan

• All working meals covered

• Relocation support for San Francisco

• Company-wide annual off‑site

• High ownership, high trust, and fast career progression alongside world-class client partners

• In‑person culture with deep commitment to excellence

This is a full-time, on-site role based in San Francisco. We do not offer hybrid or remote positions.