Senior Software Engineer; C#​/.NET

Senior Software Engineer (C#/.NET)

CoStar Group (NASDAQ: CSGP) is a leading global provider of commercial and residential real estate information, analytics, and online marketplaces. This position is located in Arlington, VA and is in office Monday through Thursday with work from home on Friday.

• Build big, distributed, API‑driven systems for tens of thousands of users.
• Design and implement AI‑powered software solutions that enhance the 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; our primary tools are C#, .NET Framework, SQL Server, AWS.
• Utilize AI models to enhance monitoring, replayability, observability, and diagnostic capabilities to improve system reliability, accelerate problem resolution, and reduce operational risk.
• 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.
• Continually evaluate emerging technologies to identify opportunities, trends, and best practices that can be leveraged to strengthen CoStar’s technology platform and development practices.

• Bachelor’s Degree required from an accredited, not for profit, in‑person university or college.
• A track record of commitment to prior employers.
• 5+ years of deep .NET development (C#) development experience including cross‑platform communication technologies such as Web API.
• Working knowledge and experience with cloud‑based platforms (AWS or Azure).
• Experience with RESTful web services and ASP.NET MVC.
• Experience in 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 working 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 family
• 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

The final salary or hourly rate offered for this role will fall within the range set forth below based on a variety of factors, including but not limited to, geographic location, skills, and competencies.
Base Compensation: $143,000 - $187,000 Annually

We welcome all qualified candidates who are currently eligible to work full‑time in the United States to apply. However, please note that CoStar Group is not able to provide visa sponsorship for this position.

CoStar Group is an Equal Employment Opportunity Employer; we maintain a drug‑free workplace and perform pre‑employment substance abuse testing.