Senior Software Engineer, Backend

About this role

At Numero, we build software for political campaigns and nonprofits. Since our founding in 2019, we’ve scaled our platform to serve thousands of campaigns ranging from city council seats to US Senate races, and have helped them collectively raise over $10B in contributions.
Our platform is an all-in-one system comprised of a donor CRM, broadcast email + texting tools, and payment processing pages that our clients rely on for their work every day. As our product is the platform that our users operate out of every day, this also means that when we build and launch new products, we do so to all of our users, at scale 🚀.
We’ve experienced tremendous growth over the past several years and are hiring experienced engineers to help us scale our backend infrastructure and to support the development of several new products on our roadmap. In joining our team, you will help shape our team’s culture and have a substantial impact on the success of our company 📈 – come join us!
Who we’re looking for
The work at Numero is challenging because of the nature of what we build: systems where a subtle edge case or an inefficient query is felt by every client, on every campaign, during the highest-traffic moments of an election cycle. We're looking for someone who finds that kind of nuance and scale genuinely fun to untangle – and who has the experience to do it well.

• Deep experience building and scaling user-facing backend systems. Ideally 6+ years, with a meaningful portion spent responsible for production systems with significant traffic. Leveling and salary will be commensurate with experience.

• A deep, instinctive understanding of how code behaves at scale. You think naturally about the code paths that get hit by millions of requests, and you reason about cost before it shows up in a flame graph.

• Real fluency with SQL and relational data at scale. You can anticipate bottlenecks and use optimizations like indexing and batching to write efficient, scalable queries. You can analyze performance metrics and monitoring after shipping to ensure things are working.

• A bias toward building things the right way. You architect patterns that scale well even when day-one usage looks small – because you've seen how "we'll fix it later" rarely survives contact with growth.

• Hands-on experience building with AI – and a hunger to get sharper at it. You already use AI tools in your day-to-day engineering and want to deepen that craft as agentic coding matures; we're investing heavily here and want teammates pushing the frontier with us.

• Excellent written and verbal communication and high EQ. On a team this small, how you reason out loud and collaborate matters as much as what you ship.

• You are located in the continental USA (ET, CT, MT, PT) and are willing to travel 1-2x a year for company retreats and/or team offsites (usually held in California).

We're a tight-knit team, energized by the challenges in our work because of how far its impact reaches – what we build touches every campaign and nonprofit on the platform within minutes of deploying. That makes the problems we tackle genuinely meaningful: the things you ship move the needle for clients running some of the most consequential campaigns in the country.
What we’re working on
Every feature of Numero is built with best-in-class engineering and design, in close coordination with our clients. Much of the work carries real complexity – money movement, compliance, and querying at scale – and because we're an all-in-one platform, most of it reaches every client the moment it ships, often at a scale of millions of requests and billions of records. A sampling of what's on our plate right now:

• Numero Agents– a suite of AI agents that let clients drive the platform in plain language instead of doing the work by hand, each equipped with the context, tools, and domain knowledge that make it sharp at its job. There's deep, ongoing work here across the shared intelligence and orchestration layer that powers these agents, the retrieval that grounds them, and the tooling they use to act – all built on our own Ruby LLM tooling.

• Scaling NumeroQL– NumeroQL serves millions of requests a day, filtering billions of records across multiple databases in realtime. Moving our highest-frequency queries onto OpenSearch is one technique we're using to push performance further, and we're actively exploring others – including traditional approaches like database partitioning and sharding.

• Tandem Fundraising– one of our most-requested features ever: splitting a single contribution across multiple recipients, with precise handling of fees, compliance reporting, refunds, and a long tail of edge cases – across both Stripe and PayPal.

• Payment Processing Optimization– This is our fastest-growing vertical, and we're focused on getting more supporters across the finish line. Two big levers: remarketing – automatically following up on abandoned checkouts by email – and letting returning donors securely save their information and reuse a payment method for faster, lower-friction giving. At our scale, every percentage point of conversion compounds across millions of donors.

• Communications– Building deeper integrations to support calling, texting, and the real-time infrastructure behind them – transcription, syncing communications data into the CRM, and conversational AI that handles the follow-up busywork for clients.

• Custom Fields– letting clients define their own fields to store and query any type of data in their CRM, with configurable data types, format validation, and performant querying through NumeroQL.

Our roadmap runs on a quarterly horizon with a lot of built-in flexibility: we follow our clients' needs and our fastest-growing revenue segments, always optimizing for what's best for them and for the company. And because we're a small team, we rotate across these product lines, so you'll get exposure to a wide range of the work.
How we work with AI
AI is core…