Senior Full-Stack Engineer - Stealth Company - Founding Engineer - Vertical AI

Antai Ventures is a Barcelona-based venture studio with presence across Southern Europe and Latam. Since 2012 we have co-founded 35+ companies including Glovo, Wallapop, Piper, PlatanoMelon, and Vitaance.

Our ventures have raised more than $1.5B in funding, have generated more than $3B in shareholder value, and currently employ more than 3,000 people.

At Antai, we partner up and invest in the best co-founders to build global companies willing to disrupt multi-billion dollar industries. In the last 12 years, we have gained experience in a variety of business models (E-Commerces/DNVBs, B2B SaaS, Marketplaces) operating in a wide range of industries including Edutech, Grocery, Healthtech, Fintech, Insurtech, Proptech, Autotech, among others.

We are looking for a Senior Full-Stack Engineer to join the founding team of one of our portfolio companies - a B2B SaaS platform that helps service companies manage the complex, day-to-day operations of their distributed frontline workforce. Think scheduling, real-time coordination, coverage resolution, time tracking, and client communication - all powered by an AI agent that can make phone calls, contact workers, and take autonomous action to keep operations running smoothly.

The vision is ambitious: build the operating system for an entire industry - starting with day-to-day operations, then expanding into deeper integrations across finance, HR, and everything else these companies need to run their business. AI isn't a feature we're bolting on - it's embedded from day one as a core capability that fundamentally changes how these companies operate.

The Role

You’ll be one of the first engineers on a small, high-ownership team building a product from the ground up. This isn’t a role where you’ll be handed tickets - you’ll be researching customer problems, crafting detailed specs, designing solutions, writing code, and shipping features end-to-end. You’ll work directly with the founders and be expected to bring strong judgment about what to build, how to build it, and when to keep things simple.

We need someone who is genuinely full-stack: comfortable across backend, database, frontend, mobile (web-based via Capacitor), and cloud infrastructure. You don’t need to be an expert in every layer, but you need the confidence and curiosity to work through problems across the entire stack, learn what’s needed, and find the right solution for the context.

Location: Barcelona, hybrid (some office days)

Employment: Full-time

Languages: Proficient English required. Spanish not required, but a basic level is a plus.

Compensation: €50-70K + equity

What you’ll work on

• Study customer problems deeply and translate insights into detailed functional and technical specs - then turn those specs into working software.

• Design and build core backend systems powering workforce scheduling, real-time coordination, and operational workflows.

• Build clean, well-structured APIs and data models that support web, mobile, and internal tools.

• Develop the worker-facing mobile experience (web-based, via Capacitor) with a focus on simplicity for low-tech-savviness users.

• Contribute to the AI agent’s backend - the infrastructure that lets it resolve coverage incidents, contact workers, and take autonomous actions.

• Manage and evolve cloud infrastructure, CI/CD pipelines, and developer tooling.

• Improve reliability, observability, and performance across the system.

• Build integrations with other business software the industry already uses - accounting, payroll, and other operational tools.

• Participate in design reviews and product decisions, bringing engineering perspective to what gets built and how.

Your first 3-6 months

You’ll ramp up fast. Here’s what that might look like:

• Immerse yourself in the domain - studying how service companies actually run their operations day-to-day, reviewing processed customer insights, and building a mental model of the problems we’re solving.

• Pick up existing specs, understand the reasoning behind them, and start shipping features from detailed functional and UI specifications.

• Start crafting your own specs - studying a problem, collaborating with the team to refine the approach, designing the implementation, and seeing it through to production.

• Build and iterate on the worker-facing mobile experience, making it intuitive for frontline workers with minimal tech experience.

• Get hands-on with the local-first sync layer (ElectricSQL, TanStack DB) as real usage reveals edge cases and design tradeoffs.

• Help shape the AI agent’s capabilities - how it reasons about coverage, contacts workers, and escalates to managers.

• Improve the development workflow itself - testing patterns, CI/CD, tooling, and the feedback loop between specs and code.

Throughout all of this, you’ll be leveraging AI coding agents heavily - not as an afterthought, but as a core part of how you research, design, plan, implement, and review.

What we’re looking for

Strong engineering fundamentals

• You’ve designed and operated production systems and understand the tradeoffs between latency, consistency, cost, and complexity.

• You write simple, maintainable code and care deeply about good abstractions. You know that simplicity is the ultimate sophistication.

• You’re comfortable owning systems end-to-end: from research and spec writing, through design and implementation, to deployment and operations.

• You have solid experience with TypeScript, SQL, and modern web frameworks. Our stack is Vue, Nuxt 4, Nuxt UI, PostgreSQL, ZenStack/Prisma, ElectricSQL, TanStack DB, and Capacitor.

• You’ve worked with cloud infrastructure (GCP, AWS, or similar) and understand CI/CD, containerization, and production operations.

AI-augmented engineering

• You use AI coding agents daily and can orchestrate multi-file agentic workflows with tools like Claude Code, Cursor, or similar - not just autocomplete, but steering complex architectural decisions and reviewing AI-generated output for quality and maintainability.

• You can effectively amplify yourself using AI across the entire development lifecycle: research, spec writing, design, implementation, code review, and debugging.

• You stay current with the AI tooling ecosystem and have opinions about what works and what doesn’t.

Product and business sense

• You can see the bigger picture. You deeply understand customers and their world, and you balance business goals and constraints in your engineering decisions.

• You anticipate problems before they arrive and know when to compromise, be pragmatic, and avoid over-engineering.

• You’re a clear communicator who can articulate technical tradeoffs to non-technical teammates and write specs that others can follow.

Zero-to-One energy

• You thrive in the earliest stages of building - where there's no playbook, priorities shift fast, and the best move is often the scrappy one that gets things done now.

• You're comfortable with high intensity and ambiguity. You don't need a perfectly defined scope to start making progress.

• You've been through the 0→1 phase before (or you're hungry for it) and you understand that speed of iteration matters more than perfection.

Nice signals

• Experience with local-first / offline-first architectures or real-time sync.

• Experience building mobile apps with Capacitor or similar web-to-native bridges.

• Familiarity with the Vue/Nuxt ecosystem.

• Experience in B2B SaaS, workforce management, or field service operations.

• You’ve worked in early-stage startups and are comfortable with ambiguity and fast-changing priorities.

• Experience integrating LLMs into production systems (function calling, RAG, agentic workflows).

How we work

• Spec-driven development. Features are designed through detailed specs before code is written. Engineering decisions are informed and deliberate, not reactive.

• AI-augmented workflow as standard practice. AI coding agents aren’t a novelty here - they’re part of how the team operates daily, across every phase of the development cycle.

• Structured async + tight real-time alignment. We use Linear for task-centered work and value deliberate, organized communication. At the same time, we stay tightly in sync through lightweight, real-time collaboration - the natural rhythm of a small team that keeps each other in the loop without meetings and status rituals.

• Direct collaboration with founders. No layers of product management between you and the people making product and business decisions.

• Small team, high standards. We optimize for learning speed and iteration velocity, not process and ceremony.

Why this role

• You’ll shape the product and architecture from the earliest stage - the systems you build will exist for years.

• You’ll work on a genuinely AI-native product where an autonomous agent is a core differentiator, not a marketing checkbox.

• You’ll have real ownership and direct impact on what gets built, how it’s built, and how fast the company moves.

• You’ll join a team that takes engineering craft seriously while staying pragmatic about what matters at this stage.

• You’ll help define what “great engineering” looks like at a company that’s just getting started.