Backend Engineer - AI Agents (all genders)

Lime Connect; Köln; On-site; EUR 90,000 - 130,000; Full time

Benefits offered by this job

Health budget

Urban Sports Club membership

Learning budget for courses

Udemy/Masterclass access

Leadership programmes (Next Gen)

Weekly FIKA & team events

International summer party

Office in Cologne MediaPark (3 days)

Mobility budget / Job ticket

Free parking at MediaPark

28 days holiday plus specials

Special leave up to 5 days

Job summary

Personio's Cologne backend team is seeking an experienced engineer to advance AI features built on language models used daily by customers. You will expand AI agents and automation, refine context management, and optimize agent loops and tool calls with a focus on robust multi-LLM workflows.

You will collaborate with Product, shape AI architecture, and ensure high-quality evals using real conversations. Proficiency in Python and Django is preferred, with hybrid office presence in Cologne.

Qualifications

• Five+ years backend experience.
• Experience building AI features with LLMs used daily.
• Proficient in Python; Django preferred.
• Experience with AI agents, context windows, tool calling, and prompting.
• Familiarity with retrieval augmented generation (RAG) and vector databases.
• Experience with evals (Langfuse, Arize Phoenix, LangSmith) or similar.
• Nice to have: Pydantic AI or LiteLLM.
• Fluent German and English.

Responsibilities

• Develop and maintain backend AI features integrated with LLMs used by customers.
• Build AI agents and automation solutions (Connect AI) and manage agent loops and tool calls.
• Shape AI architecture for flexible multi-LLM workflows.
• Implement eval pipelines to improve versions using real customer conversations.
• Provide API access and tooling (MCP tools, website crawling) for agents.

Skills

Backend development

AI features with LLMs

Python

Django

AI agents

Context windows

Tool calling

Prompting

RAG

Vector databases

Eval frameworks (Langfuse)

LangSmith

Pydantic AI

LiteLLM

German & English fluency

Tools

Python

Django

Langfuse

Arize Phoenix

LangSmith

Pydantic AI

LiteLLM

Job description

What You'll Be Working On

• Within the backend team, you're the go-to person for AI and work closely with Product.
• You further develop our AI agents and automation solutions such as Connect AI, from the agent loop and tool calling to context management.
• You help shape our AI architecture and make sure we can work flexibly with different LLMs.
• When it comes to quality, we rely on evals with real customer conversations and methods like LLM-as-a-judge. You help expand this area so every new version gets measurably better.
• Through APIs, MCP tools and website crawling, you give our agents the knowledge and tools they need.

What Makes You a Fit

• You have at least five years of backend experience, including one year building AI features based on language models that people use every day.
• Python is your tool of choice, and ideally you already know Django.
• You've built AI agents before and know context windows, tool calling and prompting from hands-on work.
• You've worked with RAG and vector databases yourself.
• You're familiar with evals, whether with Langfuse, Arize Phoenix, LangSmith or something you built yourself.
• Libraries like Pydantic AI or LiteLLM are a plus.
• You follow what's happening in AI, try things out quickly and take ownership of your topics.
• You're fluent in German and English.

What’s in It for You

HEALTH & SPORTS

• 600 € health budget per year, including 24/7 medical advice — also for family members in your household
• Subsidised Urban Sports Club membership (20 € monthly contribution)

DEVELOPMENT & GROWTH

• Learning budget for courses, books and conferences
• Free access to Udemy, Masterclass and language learning apps
• Leadership programmes such as "Next Gen" and "Effective Manager"

TEAM & CULTURE

• Weekly FIKA, movie nights, book club and regular get-togethers and team events
• International summer party together with our colleagues in the Nordics

WORK ENVIRONMENT

• Office-first setup: 3 days in our Cologne office at the MediaPark, 2 days remote
• 360° view across Cologne from the 14th floor
• Workation within the EU
• Snacks, cereal bar and drinks in the office

COMPENSATION & BENEFITS

• Company pension scheme via Zurich with a 30 % employer contribution
• Job ticket or mobility budget, plus free parking at the MediaPark
• Corporate benefits
• 28 days of holiday, plus Christmas Eve and New Year's Eve off
• Up to 5 days of special leave for important life events