About Zeffy

Zeffy is the fastest-growing nonprofit platform in North America, helping organizations raise funds, run events, and engage donors. We are already working with more than 80,000 nonprofits and are doubling annually.

Millions of people dedicate their lives to causes beyond profit, running schools, shelters, and community initiatives. Yet most still lack modern tools. We believe the greatest opportunity for technology today is to amplify the impact of nonprofits.

Built on a sustainable, self-funded model, Zeffy reaches over 1M donors monthly and grows profitably, giving us the freedom to focus fully on our mission.

Nonprofit workers are heroes. They deserve the best technology, and we’re hiring top minds and top hearts to build it for them.

About the role

As a Senior Software Developer at Zeffy, you’ll play a key role in building and scaling the the best tech for charities.

Over the past two months, our team has:

• Built a rich-text email builder from scratch — with undo/redo, block navigation, text wrapping, and a full visual editing experience, so nonprofits can write compelling donor communications without leaving Zeffy.

• Rebuilt our entire payment submission flow — separating the critical payment path from async post-processing, replacing status-based concurrency model with dedicated DB tables, and cutting timeouts that were our #1 source of support tickets.

• Engineered a custom rate limiter on top of tRPC and Redis — because Cloudflare's IP-only limiting wasn't enough at our request density. Built as a tRPC middleware with a single-script Redis lookup, reducing p95 overhead to under 80ms while actively blocking abuse patterns.

• Scaled our infrastructure to handle Giving Tuesday — our highest-traffic day of the year, without a single incident, through Node.js process clustering on Heroku dynos, bringing event loop saturation back to baseline across a 25% traffic surge.

• Introduced Funds — a data model and product feature that lets nonprofits create designated funds, assign them to campaigns, and let donors earmark their gift

You’ll take ownership on similar projects, things that go from idea to production quickly and actually matter to the people using them. You’ll make judgment calls, simplify and help teammates do the same.

As a senior developer, you’ll also help shape our processes and mentor others to maintain Zeffy’s “simple and fast” culture as we grow.

Development Principles at Zeffy:

• We always optimize the ratio impact / effort, it’s what we call Zeffy perfectionism, perfection in impact.

• We build the simplest solution first to validate ideas quickly, keeping the codebase clean without solving problems that don’t exist yet.

• We are organized in 2 months cycle, to make sure we prioritize radically. We set ourselves targets on the 4 following dimensions: efficiency, security, stability and performance.

• Trust and ownership: every target is clear and owned by one person who has full autonomy to reach it. Owned by one person doesn’t mean working alone on it.

• Continuous improvement: We regularly review and refine our processes, promoting a culture of learning and growth through feedback.

Our Stack

• Frontend: React/Next.js (Typescript)

• Backend: Nest.js (TypeScript)

• Database: PostgreSQL, Algolia

• CI/CD: GitHub Actions, Cypress

Previous experience in these technologies is not required, we’ll help you ramp up quickly through focused onboarding and internal bootcamps.

Preferred experience (qualifications)

We’re looking for someone with at least 4 years of experience as developer, ideally in SaaS or web-based products.

We move fast by keeping things simple, and we want someone who shares that mindset: experienced enough to know when to push for structure, and wise enough to know when to cut the noise and just build.

• you’ve built real products, learned from trial and error, and developed the instinct to separate what truly matters from what doesn’t.

• you bring seniority through judgment, not hierarchy — through the ability to make smart, pragmatic decisions that balance quality and speed.

• you value clarity over complexity, progress over perfection. You mentor others with empathy, share what you’ve learned, and help elevate the team without slowing it down.

If you’re fed up with unnecessary complexity — endless processes, over-engineered solutions, or meetings that don’t move the work forward — you’ll feel at home here.

💡 Research shows that candidates from underrepresented backgrounds often don't apply for roles if they don't check every box. If this applies to you and you are interested in the position, we'd love to hear from you!

What’s in it for you

• 🏖️ 5 weeks holiday + RTT per calendar year

• 💰 Competitive stock option program

• 🏥 Health insurance (with Alan)

• 🚲 Allowance for ecological transport #bike #transit

• 🤝 Team volunteering four times per year

• 🏢 Offices located in the heart of Paris 11ème, with the possibility of flexible, hybrid work

• 🌍 Offsite summit once a year with the entire team

• ✨ Work with individuals driven to make a profound and positive impact on the world!

Recruitment Process

• Call with Recruiter (45 min)

• Meeting with Hiring Manager (1.5h)

• Case Study (2h)

• Cultural interview with leadership (1h)

• Team lunch & Reference check

• Job offer