Full-Stack Developer Intern – React / Next.js | UNPAID

This is an unpaid internship. There is no salary attached to this role. Please only apply if an unpaid placement fits your circumstances and any requirements from your educational institution.

Want to use your development skills to help a sustainability venture grow? Join Treesy and help improve a live platform that connects people and businesses with tree planting.

🌱 Explore our website: https://treesy.dk

About Treesy

Our mission is to make it easier for people and businesses to support tree planting and understand their contribution.

We’re building tools that connect tree planting with everyday business activities, supported by clear calculations, accessible customer information and transparent documentation.

We care about credible sustainability communication: documented assumptions and meaningful reporting, without suggesting that planting trees automatically makes a product or activity climate-neutral.

We’re looking for a curious, proactive developer intern who wants to help turn that mission into useful digital experiences.

What you’ll help build

You’ll work directly with the founder on projects chosen around your skills, interests and internship duration. Our priorities include:

An interactive solution finder for businesses
Create a step-by-step funnel where businesses enter details such as their sector, employee count, product price and sales volume, then receive a tailored suggestion for how Treesy could fit into their business.

Suggestions might show what funding tree planting per product sold, completed project or employee would look like, including estimated costs and clear assumptions. Visitors should then be able to request a proposal with their answers already included.

A calculator for trades and construction businesses
Build a calculator inspired by our existing calculator for travel agencies. It should help businesses estimate a project’s climate footprint using documented inputs and assumptions, then calculate a corresponding tree-planting contribution. We’ll define the methodology and content together.

An improved customer dashboard
Make it easier for customers to view their subscriptions, allocated trees, planting information and downloadable documents.

Automated tree-planting certificates
Develop a reliable workflow for generating and delivering certificates based on verified customer and planting data.

SEO and AI search visibility (GEO)
Improve how search engines and AI-powered search tools discover and understand Treesy through better metadata, structured data, internal links, indexing, page structure and performance.

Pricing calculator improvements
Add an option to display prices including or excluding VAT, with clear labels and consistent calculations.

User experience and platform reliability
Integrate customer testimonial videos, improve mobile usability, simplify the sign-up journey and investigate any remaining issues in subscription payments and tree allocation.

You won’t be expected to deliver everything above. We’ll agree on a focused, realistic scope together.

Our technology

The website is built with React and Next.js 16, using:

TypeScript for application code.

Supabase for database and backend functionality.

Stripe for payments and subscriptions.

Vercel for hosting and deployment.

GitHub for version control and pull requests.

Experience with SQL, APIs, webhooks or technical SEO would be useful, but you don’t need to know every part of the stack.

Who we’re looking for

You could be a student, recent graduate or early-career developer with practical projects to show.

We’d like you to:

Have practical experience with React and JavaScript or TypeScript.

Be comfortable exploring an existing codebase and investigating problems.

Test your work and explain your changes.

Communicate clearly in English and ask questions when needed.

Enjoy suggesting improvements and following tasks through.

Be interested in sustainability and building tools people can use.

Tell us what you can already do and what you’d like to learn.

What you can expect

Hands-on experience contributing to a live product.

Direct collaboration with the founder on priorities, user journeys and product decisions.

Clearly scoped projects with visible outcomes.

Room to contribute ideas and take ownership of agreed tasks.

Experience connecting frontend interfaces with payments, data and automated workflows.

This role suits someone comfortable working independently. You’ll receive product direction and feedback, but this is not a structured training programme with daily supervision from a senior engineer.

Practical details

Compensation: Unpaid.

Hours, start date and duration will be agreed before the internship begins.

Initial responsibilities will reflect your experience and availability.

How to apply

Please send:

A short introduction and why Treesy’s mission interests you.

Your GitHub, portfolio or one or two relevant projects, explaining your contribution.

Your availability and preferred internship duration.

Your CV

Visit https://treesy.dk before applying and tell us one thing you think we could improve.