Senior Software Engineer - Fullstack

Why this role exists

You'll be the first engineer dedicated to owning those critical paths: onboarding, activation flows, monetisation infrastructure, and the experimentation systems that help us improve all of it. As JustCall expands how it serves customers - from individual sales reps to small teams to mid-market organisations running AI-powered call workflows - you'll play a central role in building the growth engine that scales with them.

We're looking for a Senior Full-Stack Growth Engineer who is excited to build those journeys end-to-end. You'll work at the intersection of engineering, product, and data to create fast, reliable growth systems that turn first-time users into activated users, and activated users into expanding accounts.

What you'll actually do

• Own and improve key product journeys from sign-up through onboarding, feature discovery, and purchase
• Build and refine onboarding experiences that help users - individual reps, team admins, growing accounts - quickly understand and realise the value of JustCall
• Design and implement self-serve billing flows: subscriptions, plan gating, trial logic, seat expansion, and upgrade paths that work without a salesperson
• Wire AI into the growth experience: personalised onboarding, intelligent nudges, value demonstrations - built to production standard
• Iterate quickly, delivering thoughtful, incremental improvements that compound over time
• Contribute to the evolution of our onboarding and discovery systems as the product and customer base continue to grow.
• Integrate third-party and AI tools that enrich the product experience.

What we're looking for

• 5+ years of full-stack engineering experience, with meaningful time on growth, self-serve, or PLG systems
• Frontend depth - solid JavaScript, HTML, CSS. You care about what users experience, not just whether the backend call succeeded
• Strong Next.js fluency - you understand SSR, CSR, and ISR and choose deliberately, not by default
• Experimentation and instrumentation fluency - you've owned a metric, designed A/B tests, and know when data is wrong before the analyst does
• Comfortable with billing systems, paywalls, and subscription logic - the backend of how products make money
• Write production-grade code with meaningful test coverage - unit, integration, and e2e. You default to TDD on critical paths and know when pragmatism is warranted
• Break ambiguous problems into clear hypotheses and ship solutions end-to-end.
• AI-first in how you work and build. High agency, curious about how customers actually use the product — you find drop-offs that data alone wouldn't show you

Our stack: NestJS · Node.js · TypeScript · MongoDB · ClickHouse · React · GCP

How we work

• Outcomes over process. We measure engineering impact by production reliability, latency benchmarks, eval coverage, and the AI experiences we ship - not tickets closed.
• Deeply hands-on culture - leadership here means staying close to the hardest technical problems, not delegating your way out of them.
• Fast cycles, high ambiguity, and the expectation that you bring both architectural depth and shipping velocity to every initiative.
• Competitive pay tied to the systems you architect and the engineering culture you build.

The bigger picture

JustCall is SaaS Labs flagship product - used by 6,000+ businesses across 70+ countries to run their customer conversations. We're backed by Peak XV and Base10 Partners, have crossed $40M ARR, and are building toward $100M with the team, the product, and the infrastructure to get there.

If this is the role you've been waiting to find - let's talk.

SaaS Labs takes pride in being an equal opportunity employer. We believe diverse teams build better products, which is why we're committed to making hiring or any employment decision regardless of race, colour, religion, national origin, age, sex, marital status, ancestry, disability, genetic information, veteran status, gender identity, sexual orientation, or any other characteristic.