Senior Full-Stack Engineer - AI Tools Development

Why join Sintra?

We build AI employees for small businesses. Real helpers with personalities, not faceless chatbots. They handle the work that keeps owners up at night - answering customer emails, posting on social media, analyzing sales data. For business owners who've always worked alone, we're giving them their first team.

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50,000+ businesses use Sintra because for the first time someone made AI actually useful for them. While Silicon Valley builds for tech companies, we're building for the florist who needs help with Instagram, the contractor drowning in invoices, the restaurant owner who can't keep up with reviews.

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This is a unique moment in history. AI just became good enough to fundamentally change how small businesses operate. Behind every business is someone trying hard for their family. Someone with one goal - put food on the table. And our job is to help them succeed.

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Having just raised our $17M seed round, we're off to the races. Small, fast-moving team building together in person. We ship daily, take ownership of what we build, and live by one principle - work is play.

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Who We're Looking For

• 4+ years shipping production full-stack applications
• Strong Python, Node.js, and React skills with focus on clean architecture
• Experience with LLM tool calling, function definitions, and prompt engineering
• Solid product thinking - you understand how technical decisions affect user experience
• Comfortable navigating large codebases and understanding service boundaries
• Track record of shipping independently while collaborating well with designers and other engineers
• Strong code review skills - you catch bugs before they hit production
• Comfortable using AI tools to accelerate development
  
  

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What You'll Do

• Create tools/functions that LLMs can reliably call - with bulletproof error handling and clear documentation
• Implement the UI for these tools, working with designers to keep it simple for non-technical users
• Build retry logic, fallbacks, and self-correction mechanisms
• Instrument everything - add tracking and logging to measure real impact. Iterate relentlessly based on data
• Develop background workflows that chain multiple operations together
• Collaborate with designers on technical constraints and possibilities
• Mentor teammates and raise the engineering bar through code reviews and pair programming
  
  

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Our tech stack

• Frontend: React
• Backend: Python with FastAPI (core), Node (microservices)
• Infrastructure: Railway, AWS, multiple LLM providers
• DevOps & Tooling: Github Actions, Grafana
  
  

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Our hiring process

• Fill in the application form. If we see a fit, we'll reach out for an intro call.
• Complete a take-home task that mirrors real work you'd do here. Be prepared to explain what you did and why.
• Join us for a tech call. Meet the team, see if we're right for each other.
• Get an offer if it's a mutual fit.
  
  

We understand good people have options, that's why we move super fast. Life's too short for drawn-out hiring processes.

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What we offer

• Compensation & Equity ‍Top-of-market salary in Vilnius plus meaningful equity, so you own part of what you build. Salary range for this role: €5,000-8,000/month depending on expertise and experience.
• Health & Wellness ‍Health insurance, gym membership with personal trainer option, team lunch at the office.
• Seamless Relocation ‍Relocation bonus and support to make your move to Vilnius smooth.
  
  

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