Senior Software Developer, Full Stack

RS21• US,

6d•$105,000 - $140,000

About The Position

The Senior Software Developer, Full Stack is an experienced technical leader who operates at the intersection of hands-on engineering execution, software architecture, client-facing solutioning, and cross-functional delivery leadership. This role is designed for an engineer who can walk into any project environment, immediately understand what needs to be built and why, design the right technical approach, align the teams, and deliver. At the Senior level, this person owns the design and delivery of complex application systems and platform services across RS21's most demanding client engagements. They architect scalable, maintainable software systems, lead cross-functional technical delivery, mentor junior and mid-level developers with genuine investment, and serve as a credible technical resource for clients across the full software development lifecycle. This role further serves as an embedded technical delivery lead for software workstreams, with the discipline to decompose complex application initiatives into structured delivery, the systems thinking to connect every engineering decision to its business outcome, and the accountability to keep multi-team delivery on track across concurrent projects. Critically, the Senior Software Developer is a force multiplier within their engagements. They raise the engineering capabilities of those around them, mentor junior and mid-level developers deliberately and generously, establish coding standards and architectural patterns across their projects, and contribute to RS21's business development efforts as a credible technical voice.

Requirements

Bachelor's degree in Computer Science, Software Engineering, or a related field; advanced degree a plus.
7+ years of hands-on software development experience, including at least 3 years in a lead or senior engineering role with ownership of complex application delivery.
Deep expertise with modern application architectures including microservices, event-driven systems, API design, and security-by-design principles.
Demonstrated proficiency in one or more backend languages and modern front-end frameworks; able to produce and govern production-grade code across the stack.
Proven ability to deliver production-grade applications on AWS using ECS/EKS, Lambda, API Gateway, DynamoDB, RDS, and S3 at client-facing scale.
Demonstrated experience integrating LLM or AI capabilities into production applications with appropriate reliability, governance, and performance standards.
Proven ability to mentor junior developers and lead technical delivery across cross-functional teams in client-facing environments.
Strong written and verbal communication skills; experienced translating architectural decisions for stakeholder audiences at multiple levels.

Nice To Haves

AWS Solutions Architect Professional or Developer Associate certification.
Experience with infrastructure-as-code tools such as Terraform or CDK and DevOps/CI-CD practices at production scale.
Experience with multi-agent orchestration frameworks and advanced prompt engineering in production deployments.
Background in consulting, professional services, or multi-client delivery environments.
Exposure to DoD, federal, or regulated-sector software environments; FedRAMP-compliant architecture experience a plus.

Responsibilities

Author scalable, maintainable application code across the full stack; set architecture patterns for active projects, establish coding conventions, and ensure that architectural decisions are documented with rationale and trade-offs.
Design and deliver production-grade application systems, APIs, and services on AWS; govern engineering standards across active projects and ensure junior engineers understand and operate to those standards.
Architect application security, including IAM design, secrets management, secure service-to-service communication, and defense-in-depth practices appropriate to the client's environment.
Architect robust CI/CD systems for assigned projects; mentor team on testing strategy, pipeline governance, release practices, and how to design deployments that fail safely.
Architect scalable container platforms using Docker and Kubernetes; mentor team on Helm, cluster governance, resource management, and workload optimization for production environments.
Lead LLM application development across complex client use cases with deep expertise in prompt engineering, chain design, tool use, and responsible deployment; mentor team on advanced prompting, evaluation, and governance.
Architect complex multi-agent systems using LangGraph, AutoGen, CrewAI, or equivalent; mentor team on reliability, observability, agent state management, and safety patterns for production deployment.
Integrate AI coding tools into team engineering workflows; coach developers on responsible use, set standards for AI-assisted code review, and shape a code quality culture that benefits from AI acceleration without depending on it.
Design and optimize application architecture for LLM-backed features; make and document decisions about latency, cost, context window management, and fallback behavior.
Lead client software discovery and requirements-gathering sessions; translate ambiguous business and operational needs into concrete, documented technical architectures with clear assumptions, trade-offs, and open questions.
Produce reference architectures, solution design documents, and technical roadmaps that guide both client delivery and internal product development; write for audiences ranging from engineering teams to executive stakeholders.
Assess and document client technical readiness for modernization, AI adoption, and platform integration; identify gaps and prescribe actionable remediation paths in terms of business impact.
Serve as a technical coordination point between client stakeholders, data engineering, data science, platform engineers, and DevOps; translate across disciplines so every team has the context they need.
Contribute to RS21 business development and proposal efforts; produce technical approach sections, architecture diagrams, and scope estimates that reflect genuine senior-level expertise.
Own end-to-end technical execution planning for software development workstreams; define the sequence of work, identify dependencies, and ensure delivery milestones map to both technical and business outcomes.
Decompose complex client initiatives into structured Jira epics, stories, and tasks with clear acceptance criteria; help junior developers understand how their individual tasks connect to the larger delivery arc.
Partner with project managers and product owners to ensure the technical execution plan stays aligned with contractual, operational, and business constraints; surface risks early with enough context for leadership to act.
Lead planning, estimation, and architecture review ceremonies with the technical authority to drive hard decisions to resolution; help teams make good choices under ambiguity.
Mentor and grow junior and mid-level developers in technical depth, architectural thinking, and engineering craft; invest in their development with the specificity and consistency that actually produces growth.
Conduct code reviews, architecture reviews, and design critiques that elevate team output quality; give feedback that is specific, actionable, and calibrated to help the recipient improve.
Build and maintain engineering standards, internal playbooks, and onboarding materials for the software engineering practice; make RS21's engineering capability portable, consistent, and independent of any single person.
Help the team understand not just what to build, but why it matters and how engineering decisions connect to client outcomes and RS21's broader technical strategy.
Collaborate with data engineers and data scientists building AI and analytics features to ensure application architecture meets data pipeline and model requirements; understand the full technical stack well enough to design for it.
Influence clients and internal stakeholders through evidence-based, technically grounded narratives; make complex architectural decisions understandable to non-technical audiences without oversimplifying.
Document software architectures, API designs, and engineering best practices to support transparency, reuse, and knowledge transfer across RS21's software engineering practice.
Contribute to RS21 business development and proposal efforts as a credible senior engineering voice; review proposal sections, contribute technical content, and help ensure RS21 wins software work worth doing.