Senior TypeScript/Node.js Developer (Swedish Ad Platform)

Are you passionate about building high-performance platforms that serve millions of users worldwide? We are looking for a Senior TypeScript/Node.js Developer to join our team and help transform a global AdTech product into a scalable, platform-first architecture.At Sigma Software, we value engineering excellence, innovation, and collaboration, offering the opportunity to work on cutting-edge projects with world-class customers.You will have the chance to work with advanced AWS serverless solutions, contribute to strategic architectural decisions, and enjoy a supportive environment with professional growth opportunities.CUSTOMEROur Customer is a Sweden-based AdTech company specializing in advanced self-serve advertising platforms that automate direct transactions between advertisers and major global publishers. Their technology removes traditional friction in ad sales by enabling automation, transparency, and operational efficiency at scale. Platforms are trusted by internationally recognized publishers including TripAdvisor, Bloomberg, The Washington Post, Opera, and Dow Jones, handling millions of transactions worldwide. PROJECTThe project is a strategic architectural transformation toward a Platform-First approach. The company is transitioning from monolithic, client-specific implementations to a standardized, API-driven, multi-tenant ecosystem of reusable microservices. These services power the entire product suite, remaining independent, scalable, and decoupled from frontend or customer-specific customization.Key Technologies: TypeScript, Node.js, AWS Lambda, API Gateway, DynamoDB, EventBridge, IaC tools (CloudFormation or Terraform), RESTful/GraphQL APIs.RESPONSIBILITIESOwn and govern API design by defining and maintaining strict OpenAPI specifications before implementation beginsDesign and implement high-performance microservices using TypeScript and Node.js within a serverless AWS architectureDrive FinOps excellence by architecting solutions with AWS Lambda, API Gateway, DynamoDB, and EventBridge to achieve a Scale-to-Zero cost modelEnforce logical isolation patterns across services, ensuring strict tenant data separation via JWT policies and Row-Level SecurityMaintain adherence to the Ad Context Protocol (AdCP) across all data models for consistent AdTech data languageDevelop reusable “Golden Path” templates, shared libraries, and engineering best practicesConduct rigorous code reviews focusing on latency (<200ms), availability (99.99%), and observabilityTranslate product and commercial requirements into scalable technical specificationsContribute to evolving the overall platform architecture toward standardization and reusabilityREQUIREMENTSAt least 7 years of production experience as a Back-End DeveloperStrong hands-on expertise with TypeScript and Node.jsProven experience designing API-first microservice architecturesDeep expertise in AWS serverless ecosystem: Lambda, API Gateway, DynamoDB, EventBridge, and IaC tools (CloudFormation or Terraform)Solid AdTech domain knowledge, including advertising data models and workflowsExtensive experience designing RESTful and GraphQL APIs with versioning, backward compatibility, and documentationStrong understanding of multi-tenant architecture and logical data isolation patternsExperience building standardized platforms for multiple clients instead of custom solutionsStrong focus on performance, reliability, and observability in distributed systemsAt least an Upper-Intermediate level of EnglishWILL BE A PLUSExperience as a Lead Back-End DeveloperPERSONAL PROFILEProactive and detail-oriented with a strong sense of ownershipEnjoys solving complex architectural challengesThrives in collaborative, cross-functional teamsCommitted to delivering high-quality solutions meeting demanding performance and reliability standards