Backend Engineer

JobFluent; Barcelona; Híbrido; EUR 70.000 - 110.000; Jornada completa

Ventajas ofrecidas por este puesto de trabajo

Stock options

New office on Gran Via (Barcelona)

Flexible benefits: transport, meals, &

Health insurance

Work with founders in AI startups

Descripción de la vacante

Cala AI, based in Barcelona, seeks an experienced Backend Engineer to own end-to-end backend systems powering AI-driven verification at scale. You will develop services in Python (FastAPI), design data stores across SQL/NoSQL, and scale pipelines in a fast-moving startup.

Hybrid in Barcelona (Gran Via office, 3 days/week). Stock options and flexible benefits are offered as part of a competitive package. You’ll collaborate with a tight team building trustable AI systems with real impact.

Formación

• 4+ years hands-on backend engineering experience.

Responsabilidades

• Design and build backend services using Python (FastAPI).
• Architect data storage and retrieval systems using SQL and NoSQL technologies (Postgres, Redis, Cassandra, graph databases).
• Develop and maintain scalable pipelines (batch and streaming).
• Work with cloud infrastructure on AWS and containerized environments (Kubernetes).
• Experiment with emerging AI engineering tooling (coding agents, MCP ecosystems, etc.).
• Collaborate on system design and cross-functional architectural decisions.
• Contribute to a culture of clean, pragmatic, high-quality engineering.

Conocimientos

Python

FastAPI

Distributed systems

APIs

PostgreSQL

Redis

Cassandra

Graph databases

AWS

DevOps

Data pipelines

Descripción del empleo

Cala is looking for a Backend Engineer with 4+ years of experience to build the systems behind AI-driven information verification at scale

The team behind Vilynx, a Barcelona AI startup that Apple acquired, founded Cala. They’re building a verified knowledge graph for AI agents, and they’re looking for someone who is strong in backend work (Python, APIs, distributed systems) and also enjoys working on data, infrastructure and applied AI.

Hybrid in Barcelona (3 days/week at their new office on Gran Via)

Competitive salary + stock options

Perks: flexible benefits for transport, meals and health insurance, plus a hiring process built on conversations with no coding tests

It’s a good opportunity for someone who likes owning systems end to end and wants to join an early-stage AI company.

About Cala AI

From the creators of Vilynx - a Barcelona AI startup acquired by Apple - comes Cala AI: a bold new venture redefining how information is verified and represented at massive scale. Based in Barcelona’s vibrant tech hub near Passeig de Gràcia, Cala AI is building innovative AI systems focused on trust, accuracy, and impactful technology that challenges industry norms.

Recently, Cala AI was named by Creandum to their #EuroSeed50 list - highlighting the most promising early-stage startups in Europe - an honor that reflects the strong belief in our mission and team. We are a small, ambitious group dedicated to building real solutions with grit, heart, and a culture of authenticity.

We are now growing our engineering team with an experienced Backend Engineer who enjoys working across boundaries - backend, data, infrastructure, and applied AI.

About the role

We’re looking for an experienced backend engineer with depth.

You’ll come from a Backend Engineering background - Python, APIs, distributed systems - but what matters most is your motivation to build across layers and solve complex problems end-to-end. Backend is your anchor, but this is a high-impact engineering position for someone who enjoys working with multiple parts of the system rather than in a narrow specialization.

You’ll work closely with our core team to design, build, and scale the backend systems that power large-scale AI-driven information verification and representation.

What you’ll do

• Design and build backend services using Python (FastAPI)
• Architect data storage and retrieval systems using SQL and NoSQL technologies (Postgres, Redis, Cassandra, graph databases)
• Develop and maintain scalable pipelines (batch and streaming)
• Work with cloud infrastructure on AWS and containerized environments (Kubernetes)
• Experiment with emerging AI engineering tooling (coding agents, MCP ecosystems, etc.)
• Collaborate on system design and cross-functional architectural decisions
• Contribute to a culture of clean, pragmatic, high-quality engineering

Things we value

Strong background in:

Technical stack we commonly work with:

• Python
• FastAPI or similar frameworks
• AWS
• SQL and NoSQL databases (Postgres, Redis; Cassandra or graph databases are a plus)
• Search systems or information retrieval is a nice to have
• DevOps practices

Profile:

• 4+ years of hands-on backend engineering experience, with real depth - you’ve gone deep, not wide and shallow
• Able to reason about and justify your technical decisions: pros, cons, why A over B
• Builders at heart: hackathons, side projects, open-source contributions, active GitHub are all highly appreciated
• Curious about how things work end-to-end, including the parts adjacent to your own - infrastructure, data, the systems your code runs on
• Curious about the AI ecosystem and modern developer tooling
• Comfortable in a fast-moving startup environment
• C1+ level in either English or Spanish (fluency in either is acceptable)

We are intentionally building a diverse team. We strongly encourage applications from women, underrepresented groups in tech, and individuals from non-traditional or less represented backgrounds. Diverse perspectives are critical to building responsible AI systems.

If you’re excited about the role but don’t meet every requirement, we’d still love to hear from you.

• Stock options
• New office on Gran Via (Barcelona), with a full dedicated space for Cala AI
• Flexible benefits covering transport, meals, and health insurance
• Work alongside founders with a proven track record in AI startups
• Build foundational AI systems with an "AI for good" focus
• High ownership, high autonomy, real technical challenges
• Join at an early stage and help shape both technology and culture
• A supportive, inclusive, and horizontal team environment

Hiring Process – Conversation-Based (No Coding Tests)

• Initial chat with team member focused on experience and projects
• System design interview with CTO (onsite preferred)
• Cultural fit conversation with CEO
• Offer