Full Stack Engineer III

Ready to make a serious impact? Millions of people already rely on Calendly, and we’re still in the midst of exciting product growth — it’s a fantastic time to join us. Everything you’ll work on here will accelerate your career to the next level. If you want to learn, grow, and do the best work of your life alongside the best people you’ve ever worked with, then we hope you’ll consider allowing Calendly to be a part of your professional journey.

Millions of people use Calendly to book meetings, and most of that happens on public booking pages where anyone with a link can schedule time. That openness is what makes Calendly easy to use, and it’s also what makes it a target. The Trust & Safety team keeps Calendly safe without slowing anyone down.

We protect everyone who interacts with Calendly: the hosts who share their links, the invitees who book with them, and the email and SMS providers and partners who rely on us to send responsibly. Our work covers three areas: preventing and responding to abuse, protecting the deliverability and compliance of the messages Calendly sends, and keeping messaging costs predictable as the platform grows.

Most of our problems are adversarial. We often can’t rely on knowing who someone is, so we judge behavior, patterns, and content instead. Attackers change tactics all the time, so we build signals that last from one attack to the next. And we take false positives seriously, because blocking a real customer costs more than letting a spammer through. Engineers work closely with our Trust & Safety Operations team, who see abuse first and shape what we build.

In this role, you will report to the Engineering Manager for the Trust & Safety team.

On a typical day, you will be working on: 

• Building and improving the systems that detect and stop abuse across sign-up, booking, and messaging, such as spam, phishing, bots, and fraudulent SMS traffic.
• Improving the reliability, deliverability, and compliance of the email and SMS notifications Calendly sends.
• Shipping new detection carefully: measuring how it performs on real traffic before it acts on accounts, and weighing false positives against false negatives.
• Responding to active abuse, including during on-call, by stopping the damage fast, then replacing quick fixes with durable ones.
• Building tools that help our Trust & Safety Operations team review accounts faster and understand why the system took each action.
• Partnering with Product, Operations, and Data to define requirements and measure the impact of what we ship.
• Working with other product teams to add protections to the flows they own.
• Reviewing implementation plans and pull requests, and sharing what you learn with the team.

• 3+ years of professional software development experience at a SaaS or technology company, including building and running production systems.
• Strong backend skills: building services, APIs, and data-heavy workflows in a service-oriented architecture.
• Experience with Rails, Node/TypeScript, Go, or a comparable language or framework, and a willingness to work across more than one.
• Comfort with relational databases and SQL, and with using data to check whether a change actually worked.
• An analytical, curious mindset: you think about how a system could be misused, not only how it’s supposed to be used.
• Good judgment about trade-offs, such as stopping bad actors without adding friction for real customers.
• A commitment to clean, reliable, maintainable code, thoughtful testing, and shipping in small increments.
• Clear communication with engineers and non-engineers alike, including Operations and Support partners.
• Comfort and skill with AI tools in your engineering work, including reviewing their output critically.
• Availability to take part in an on-call rotation for critical services.
• Authorized to work lawfully in the United States of America as Calendly does not engage in immigration sponsorship at this time.

• Experience in trust and safety, fraud, spam, or abuse prevention.
• Experience with email or SMS delivery, such as deliverability, sender reputation, or messaging compliance.
• Experience with bot protection, rate limiting, or third-party risk and verification services.
• Experience building rules engines, risk scoring, or ML-backed decisions in production.
• Experience using LLMs to classify or moderate user-generated content.
• Experience with GCP, Kubernetes, PostgreSQL, or Redis.

This role may require occasional travel for company events, team collaboration, or offsites.