TLDR;

Langfuse is building open source dev tooling for LLM apps based on observability/tracing. We have significant traction and are growing fast. We are looking for a backend engineer to help us scale our product. We work on-site from Berlin, Germany.

About Langfuse

Langfuse is building the open-source LLM engineering platform. We help engineers understand how users interact with their LLM applications and how they can improve them. Have a look at our website, our GitHub and especially our technical docs to learn more.

We have raised a $4m seed round from Y Combinator, Lightspeed and General Catalyst. Thousands of engineers use Langfuse to observe, debug and improve their LLM apps. We are looking for a backend engineer to join our team in-person in Berlin, Germany.

What you will be working on

Your main responsibility will be to ensure that the Langfuse platform scales. At the core of Langfuse lies the ingestion of millions of events a day via our SDKs. Once the data is in our database, we visualize it in our UI and run async workflows on top of it in the background.

You will be working closely with Max (CTO) and Steffen who ensure the uptime and resilience of Langfuse.

Here, you can find a long, in-depth blog post about a large backend challenge we recently tackled. If this sounds like something you would enjoy — we should talk!

Projects we have worked on in the past that you would have been involved in:

Optimizing the latency of complex database queries in Postgres or Clickhouse
Helping our customers deploy Langfuse in self-hosted, e.g. by updating our k8s helm chart
Adding Redis queues and a worker container to our stack to execute async tasks
Building a POC to try out Clickhouse for our needs
Re-building our SDKs to execute networking fully asynchronous
Write Terraform code to scale Langfuse containers according to custom metrics

Stack: Frontend and Backend in Typescript (including Express, NextJs, Tailwind, Prisma, tRPC), Clickhouse, Postgres, Redis, S3, Client facing SDKs in Python and Typescript, — you should be familiar with a majority of these but we trust that you can pick up a new language/framework quickly. Please have a look at our repo to see our architectural choices.

The opportunity

Join a pure-play open source devtool company in Berlin, Germany.

You are joining early. We will treat you as a core member of the team from day 1 and you will be incentivized as such. Your decisions and code lie at the foundation of our product. Choosing appropriate yet scalable technologies and anticipating upcoming challenges are key.

You will contribute to a thriving commercial open source project and build in public. You will own parts of the Langfuse product end-to-end. You may decide to take on manager responsibilities over time if you choose to.

Who We Are Looking For?

This is the perfect role for an experienced engineer that wants to join an early stage company and build it into the leading open source LLMOps platform.

You are a hard worker and thrive working in a small and accountable team
You want to take ownership in building out the infrastructure of a fast growing devtool
You have been a core maintainer of a highly reliable and scaling infrastructure
You are excited about open source software. You want to talk to our users to understand why they use us and what they require.
You have 3+ years of experience in backend or full-stack development and know the trade offs of handling large amounts of data- a CS/quantitative degree is preferred
You have impressive achievements from previous careers and from side projects — we’re excited to hear about these!

Bonus Points

You’ve started a company before or worked at a very early stage startup
Experience with or interest in SDK design and DX
ML/AI experience

Team, Values & Benefits

You will join our early core team and work closely with the three founders of Langfuse: Max (CTO), Marc (CEO) and Clemens (COO) and our team (Marlies, Hassieb, Steffen and Jannik).

We work in-person from our lovely office in the heart of Berlin-Mitte. You must be willing to be located in Berlin. We aim for 4-5 days in the office a week.

Our team culture is built around performance and learning. We want to build a small team of highly motivated, independent and intelligent people. We will support and challenge you while granting you autonomy.

A few tidbits that might help you understand what kind of company we are:

We plan on only hiring engineers for the foreseeable future
You can expect to have ~1 meeting a day on average
Reed Hastings’ ‘No Rules Rules’ inspires our culture, here’s a summary
We’re big fans of Y Combinator and follow its ethos. We’re a Silicon Valley Startup in Berlin - more here (we brought out the entire team to San Francisco for two weeks this year, we’d love to do this again!)

Salary & Equity Ranges

Salary: 70,000 - 130,000 EUR

Equity: 0.1% - 0.35% Equity

Hiring Process

Intro Call - Intro, Logistics & Fit with a founder (30min)
Second Call - Get to know Product and Tech at Langfuse with a founder (40min)
Third Call - Technical Interview: Coding challenge and Systems Design (90min)
On-site Super Day (0.5-1 day)
- We will get together in our office in Berlin and work together on a real problem for a day (we pay for your travel if required).
- This will include discussing the problem, scoping a solution and implementing a solution (or a solution sketch) and releasing it on our open source repo the same day.
Decision & Offer

We expect you to have used Langfuse (you can sign up for a free account here) and skimmed through our documentation and public content.

Compensation: €70K – €130K • 0.1% – 0.35%

• Base Salary + Equity €70K – €130K • 0.1% – 0.35%