Full Stack Engineer

This role owns a specific operational domain at Tree-Nation end-to-end - either environmental operations (project evaluation, monitoring, impact data flows) or revenue operations (CRM architecture, B2B pipeline logic, integration monitoring). That means backend services, APIs, data models, and the interfaces that internal teams and external users actually interact with. You'll work alongside a tech team of 3-5 engineers, reporting directly into the core of the company. Your job is to map what exists, identify where well-designed systems can replace fragile or manual workflows, and then build and ship them in production - from database schema to user-facing UI.

• Map the operational flows of your domain - identifying what is manual, fragile, repeated, or ripe for automation - before proposing any solution.
• Define system scope precisely: not "fix the pipeline" but "a service that qualifies inbound leads based on company size, integration type, and engagement signal, routing to human review when confidence is below threshold."
• Design modular backend services with discrete inputs, business rules, and outputs - isolated, independently deployable, observable, and replaceable.
• Model the data first: design database schemas as the operational backbone of your domain before writing application code.
• Structure data flows between internal systems, the platform database, CRMs, billing tools, and external APIs.
• Build and ship backend services and APIs in production, with clear orchestration logic and well-defined human control points.
• Own features end-to-end: design the data model, build the backend service, expose the API, and ship the frontend interface that makes it usable - without throwing work over a wall.
• Develop and maintain UI across the Tree-Nation web platform (Vue.js) and mobile app (React Native) - building interfaces that are clean, functional, and consistent with the product experience our users expect.
• Build the internal tools and dashboards that let non-technical team members monitor, validate, and act on what your systems produce.
• Prototype fast, then industrialize - using whatever stack solves the problem. Our backend is PHP, our frontend is Vue.js, and we also use TypeScript - but we don't have a sacred stack.
• Own observability and failure handling from day one, not as an afterthought.
• Be the accountable engineer for your domain's architecture - contributing to how its KPIs are defined and ensuring every technical decision reflects its operational consequence.

Days 1-30 - Understand the system. Map your domain. Interview the people who currently run the workflows you will eventually systematize. Identify the three highest-leverage points for engineering intervention. Days 30-60 - Design the architecture for the first service. Define data models, inputs, business rules, outputs, failure modes, and human control points. Align with the tech team and ship a first working version into production. Days 60-90 - Iterate based on real usage. Define the KPIs for your domain with relevant stakeholders. Begin scoping the next system.

• Strong backend engineering background - you have designed, built, and shipped production systems end-to-end.
• Deep database design thinking: you model data before you write code and understand how schema decisions propagate into downstream behavior.
• Experience with modular service architecture - systems that are scoped, isolated, composable, and replaceable.
• Solid system design instincts: APIs, state management, integration patterns, failure handling, and observability.
• Genuine full-stack experience: solid backend skills (PHP, RESTful APIs, database design) and confident frontend work (Vue.js, building interfaces that are actually pleasant to use). You don't specialize in one half and tolerate the other.
• Tool-agnostic approach - you choose the right tool for the problem and are comfortable building custom when off-the-shelf doesn't fit.
• You diagnose before you prescribe - the right solution starts with the right question, and you can sit with ambiguity long enough to understand a problem fully before proposing a fix.
• You can translate a business process into a system design - and back - and you understand that a bad data model creates bad decisions downstream.
• Comfortable talking to non-technical stakeholders, asking operational questions, and making system decisions that reflect business reality.
• Based in Barcelona and comfortable working on-site.

Nice to Have

• Experience with React Native - our mobile app is built on it and any familiarity is a head start.
• Practical exposure to LLM integration: context management, prompt reliability, output validation, and latency constraints.
• Experience with multi-agent workflows, automated pipelines, or agentic task orchestration.
• You choose AI tooling when it is the right fit for the specific problem - not because it is the interesting choice.

Mindset

• High ownership - you take initiative, but you also know when to listen first. Tree-Nation does things differently, and the best people here understand context before trying to change it
• Open and direct communicator - we give each other honest feedback because we want everyone to grow, and we expect the same openness in return.
• Systems thinker - you look for the root cause, not the quick fix. You build processes that work at scale, not band-aids that break at 50 accounts
• Self-driven and curious - you're motivated by the impact of your work, and you actively seek out better ways to do things
• Mission-aligned - reforestation isn't a marketing line for you. It's the reason you're reading this

• Competitive base salary benchmarked to Barcelona's tech market
• Permanent contract, * Flexible Remuneration Card covering meals and transport
• Wellhub (former Gympass) membership
• Access a private health insurance plan at a preferential rate negotiated by the company.
• Regular team-building events - dinners, offsites, and the occasional non-tree-related adventure
• Flexible start time between 8:00 and 10:00 and short Fridays

The Tree-Nation Difference

• Your lifetime carbon emissions are offset through monthly tree planting from the day you join
• Personal tree-planting allocation to plant and gift trees, however you choose
• A sustainability-designed office in Barcelona built to reflect the mission you're working toward
• A small, high-trust team where your work has a visible impact from day one - you'll work directly with the CEO and Growth team, not through layers that filter your input
• Direct exposure to product, tech, and strategic decisions
• A place where failure is part of the process - if nothing is failing, we're not pushing hard enough

If something clicked while reading this - the mission, the way we work, t...

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Tree-Nation is the world's largest reforestation platform, connecting citizens and companies with verified planting projects across the globe. Since 2006, over 800,000 users and 30,000+ companies have planted more than 45 million trees through our platform, across 40+ active reforestation projects worldwide. We combine technology and environmental impact to make reforestation simple, transparent, and scalable. Our goal is to plant 1 trillion trees by 2050 and we're building the platform, the automation, and the systems to get there. The Team - What We Are Made Of Our team spans many nationalities, backgrounds, and disciplines. What we share is a mindset: we take ownership because we care about what we're building, we don't back down from hard problems, and we trust each other to lead, make decisions, and ask for help when needed. We are investing heavily in automation and AI to scale our impact. The company provides access to the latest LLMs - including Enterprise Claude, ChatGPT, Gemini, and more - and we strongly encourage everyone to innovate. We're based in Barcelona and work primarily from the office, because the energy of working side by side matters to us. Tree-Nation has a platform, a database, running integrations, and active business units. The system exists - and it needs an engineer who can own a strategic piece of it. This is a new role created to bring dedicated backend ownership to a specific operational domain: designing its data models, service layer, and integration points from the inside out. We are not hiring someone to rewrite everything. We are hiring someone who diagnoses before they prescribe - and then builds things that last.