Senior Backend / AI Systems Engineer - Spellbook

About Spellbook

Spellbook is the most comprehensive AI copilot for transactional lawyers. It works directly inside Microsoft Word to help legal teams draft, review, and negotiate contracts up to 10x faster and with greater precision. Today, more than 4,000 law firms, in-house teams, and solo practitioners rely on Spellbook to simplify their workflows and eliminate the drudgery of everyday contract work.

We are backed by leading investors including Khosla Ventures, Thomson Reuters Ventures, Inovia Capital, The LegalTech Fund, Bling Capital, and Moxxie Ventures. The company recently raised $50 million in Series B funding, led by Keith Rabois at Khosla Ventures, bringing its total funding to more than $80 million.

The Role

You’ll build the backend systems that power Spellbook’s product experiences, including both traditional software services and AI-driven workflows. This is a hands-on, high-ownership role for an engineer who cares about product outcomes and understands what requires scale vs what does not, and can turn ambiguity into robust systems that lawyers trust.

The Tech Stack

Node.js, TypeScript, Express, tRPC, MongoDB, Docker, AWS, CDK, LLM providers (OpenAI, Anthropic, and others)

Responsibilities

• Build and scale backend systems that support core product functionality across Spellbook (Reviews, Chat, Library, and more).
• Design low-latency, high-reliability search, inference, and orchestration layers for AI features.
• Build and operate RAG retrieval at scale with production-grade performance optimization and permissions-correct data isolation.
• Own core platform concerns for AI: rate limiting, retries, consistency, fallbacks, safe degradation.
• Partner closely with Product and Design to make good tradeoffs between latency, accuracy, UX, and reliability.
• Use modern development workflows, including agent-assisted coding, to accelerate delivery while maintaining rigorous review, testing, and security standards.
• Participate in on-call and incident response as needed, and improve feature reliability in the process.

Qualifications

• 5+ years of experience building backend systems in production.
• Strong fundamentals in backend engineering and distributed systems: APIs, data modeling, concurrency, queues, AI inference.
• Strong NoSQL (ideally MongoDB) data modeling and performance tuning: schema design/denormalization tradeoffs, indexing strategy, query optimization, and profiling/diagnosing bottlenecks in production.
• Ability to take an ambiguous, high-impact problem from “we should do something here” to a clear plan and shipped outcome.
• Strong communication skills with the ability to write and explain technical decisions clearly to engineers and non-engineers.
• Self-starter and problem-solver motivated by curiosity, continuous improvement, and helping others succeed.
• Pragmatic approach with an understanding of where to draw the line on what needs to scale.
• Team player eager to fix issues, support team success, and improve workflows.

Nice to Haves

• Experience building LLM-powered systems in production, including prompt iteration, tool/function calling, retrieval patterns, and agent orchestration.
• Experience operating high-scale retrieval systems (vector + lexical search) and measuring/tuning retrieval quality and latency in production.
• Experience building evaluation frameworks (quality metrics, dataset curation, regression testing).
• Experience with AWS CDK and operating production services in AWS.

Why Join Spellbook?

• Embrace autonomy and accountability in a flexible, remote work environment focused on outcomes.
• Company-paid group benefits for you and your family, including $1,000 towards mental health support.
• Disconnect during holiday closures and enjoy generous time off policies.
• Monthly paid meals, annual wellness allowance, and parental leave top-ups.
• Competitive stock option grants as a pivotal early employee.