Software Engineer; C#​/.NET

Software Engineer (C#/.NET) Overview

CoStar Group (NASDAQ: CSGP) is a leading global provider of commercial and residential real‑estate information, analytics, and online marketplaces. Included in the S&P 500 Index, CoStar Group is on a mission to digitize the world’s real‑estate, empowering all people to discover properties, insights and connections that improve their businesses and lives. We have been living and breathing the world of real‑estate information and online marketplaces for over 35 years, giving us the perspective to create truly unique and valuable offerings to our customers.

We’ve continually refined, transformed and perfected our approach to our business, creating a language that has become standard in our industry, for our customers, and even our competitors. We continue that effort today, always working to improve and drive innovation. This is how we deliver for our customers, our employees, and investors. By equipping the brightest minds with the best resources available, we provide an invaluable edge in real‑estate.

As a Software Engineer on the Platform Development team, you will play a key role in expanding the data platform that supports all of CoStar Group’s largest brands including CoStar Suite, Loop Net,  and  You will deeply understand what drives the business for which you are building software. We firmly believe that what separates a good developer from a great one is a deep understanding of the business that they are supporting.

CoStar is investing heavily in artificial intelligence to accelerate software delivery, improve platform observability, automate research and business workflows, enhance product experiences through intelligent agents and skills, and improve data quality across enterprise systems. Successful candidates will demonstrate a willingness to learn, adopt, and apply AI technologies responsibly to solve complex business and engineering challenges. 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.
• 3+ years of deep .NET development (C#) 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…