Senior Software Engineer; C#​/.NET

Senior Software Engineer (C#/.NET)

Location:

Arlington, VA – in‑office Monday through Thursday, work from home on Friday.

CoStar Group (NASDAQ: CSGP) is a leading global provider of commercial and residential real‑estate information, analytics, and online marketplaces. As part of the S&P 500 Index, CoStar Group’s mission is to digitize the world’s real‑estate industry, empowering people to discover properties, insights, and connections that improve their businesses and lives. With over 35 years of experience, CoStar continually refines its approach to leverage artificial intelligence for accelerated software delivery, improved platform observability, smarter workflows, and enhanced product experiences.

• Build large, distributed, API‑driven systems for tens of thousands of users.
• Design and implement AI‑powered software solutions that enhance customer experience, improve platform intelligence, and unlock new product capabilities across CoStar brands.
• Build and integrate AI skills, agents, tools, and intelligent workflows into internal systems and customer‑facing applications.
• Produce bullet‑proof code that is robust, efficient, and maintainable using C#, .NET Framework, SQL Server, and AWS.
• Utilize AI models to enhance monitoring, replayability, observability, and diagnostics, improving system reliability and accelerating problem resolution.
• Implement telemetry‑driven solutions that proactively identify anomalies, performance bottlenecks, and potential customer‑impacting issues.
• Drive and lead software design, development standards, and code reviews.
• Build intelligent automation solutions that streamline research workflows, improve information discovery, and increase operational efficiency across business functions.
• Collaborate with Product, Research, and Data teams to identify opportunities where AI‑driven automation can create business value and improve decision‑making.
• Continuously evaluate emerging technologies to identify opportunities, trends, and best practices that strengthen CoStar’s technology platform and development practices.

• Bachelor’s degree from an accredited, not‑for‑profit, in‑person university or college.
• A track record of commitment to prior employers.
• 5+ years of deep .NET (C#) development experience, including cross‑platform communication technologies such as Web API.
• Working knowledge of cloud‑based platforms (AWS or Azure).
• Experience with RESTful web services and ASP.NET MVC.
• Experience architecting, designing, and building large‑scale distributed, service‑oriented systems and web applications in an agile environment.
• Data modeling experience.
• Familiarity with large language models (LLMs), prompt engineering, or agent‑based architectures.
• Experience with monitoring, telemetry, observability, or automated diagnostics platforms.
• Strong understanding of data quality principles, data governance concepts, and data‑centric application design.

• Strong communication skills to both business and technical partners.
• SQL and database development knowledge.
• Familiarity with AWS PaaS services such as Lambda, DynamoDB, and SQS.
• Data modeling experience from conceptual, logical, and physical designs.
• Experience implementing AI agents, workflow automation platforms, or intelligent search solutions.
• Experience applying AI‑assisted software development practices to improve engineering productivity and code quality.

• Comprehensive healthcare coverage: medical, vision, dental, prescription drug, life, legal, and supplementary insurance.
• Virtual and in‑person mental health counseling services for individuals and families.
• Commuter and parking benefits.
• 401(k) retirement plan with matching contributions.
• Employee Stock Purchase Plan.
• Paid time off.
• Tuition reimbursement.
• On‑site fitness center and/or reimbursed fitness center membership costs (location dependent).
• Access to CoStar Group’s Employee Resource Groups.
• Complimentary gourmet coffee, tea, hot chocolate, fresh fruit, and other healthy snacks.

Base Compensation: $143,000 – $187,000 annually.

CoStar Group is an Equal Employment Opportunity Employer; we maintain a drug‑free…