Senior AI-Native Systems Engineer

Justworks; United Kingdom; On-site; GBP 132,000 - 170,000; Full time

Job summary

Justworks is hiring a Senior Software Engineer in the United Kingdom to join a small, autonomous cross-functional team building AI-native agent platforms. You’ll own core platform components, design APIs, and shape knowledge infrastructure while collaborating with Operations to automate workflows.

You’ll mentor peers and help ship production-grade systems used by customers daily. You will work in a fast-paced, early-stage environment, balancing quality with speed and maintaining a product-minded

Qualifications

• 5+ years of backend engineering experience building and operating production systems.
• Hands-on experience with LLMs and AI agents (orchestration, RAG, tool/function calling, or similar).
• Strong API design and system integration skills.
• Product-minded: questions requirements and contributes to product decisions, not just execution.
• Proven ownership of complex projects in ambiguous, early-stage environments.

Responsibilities

• Design, build, and own core components of the agent platform, from the orchestration layer to the tool integrations connecting it to internal systems.
• Build and evolve the capabilities layer: APIs, data access patterns, and service integrations for agents to execute operational workflows.
• Architect the knowledge and memory infrastructure, allowing agents to retrieve the data and act across our systems.
• Design and implement the trust and safety framework, including audit trails, human-in-the-loop controls, and guardrails for safe and auditable AI-driven operations.
• Contribute to agent evaluation and testing infrastructure, defining how we measure accuracy, reliability, and regression across agent behaviors.
• Partner directly with Operations to understand workflows, identify automation opportunities, and translate process knowledge into agent capabilities.
• Mentor other engineers on the team as it grows.

Skills

Backend engineering

Product thinking

Ownership mindset

Tools

Golang

Ruby on Rails

Javascript

Java

C#

Python

VueJS

MySQL

Kafka

AWS

Git

Memcache

Redis

ElasticSearch

Docker

Terraform

Kubernetes

CircleCI

DataDog

Job description

Justworks is hiring a Senior Software Engineer in the United Kingdom to join a small, autonomous cross-functional team building AI-native agent platforms. You’ll own core platform components, design APIs, and shape knowledge infrastructure while collaborating with Operations to automate workflows.

You’ll mentor peers and help ship production-grade systems used by customers daily. You will work in a fast-paced, early-stage environment, balancing quality with speed and maintaining a product-minded