Senior Software Engineer (C#/.NET)

CoStar Group, Inc.; Arlington (VA); Hybrid; USD 143,000 - 187,000; Full time

Benefits offered by this job

Healthcare

401K with matching

Tuition reimbursement

Employee stock purchase plan

Paid time off

On-site fitness center

Employee Resource Groups

Snacks and beverages

Job summary

CoStar Group, located in Arlington, VA, is seeking a Senior Software Engineer to extend the data platform across its brands. The role emphasizes building distributed, API-driven systems with C#, .NET, SQL Server, and AWS, while integrating AI agents and automation to improve intelligence and efficiency.

You will collaborate with Product, Research, and Data teams and help define standards for scalable, observable services in an Agile environment.

Qualifications

• Bachelor’s Degree from an accredited university.
• 5+ years of deep .NET development (C#) with Web API.
• MSSQL or other relational database development experience.
• Cloud platforms (AWS or Azure) experience.
• RESTful web services and ASP.NET MVC experience.
• Experience building large-scale distributed, service-oriented systems in an agile environment.
• Data modeling experience.
• Familiarity with LLMs, prompt engineering, or agent-based architectures.
• Experience with monitoring, telemetry, observability, or diagnostics platforms.
• Strong understanding of data quality principles and data governance.

Responsibilities

• Build big, distributed, API-driven systems for tens of thousands of users.
• Design and implement AI-powered software solutions across CoStar brands.
• Build and integrate AI skills, agents, tools, and intelligent workflows.
• Produce bullet-proof code using C#, .NET Framework, SQL Server, AWS.
• Utilize AI models to enhance monitoring, observability, and diagnostics.
• Implement telemetry-driven solutions to identify anomalies and bottlenecks.
• Lead software design, development standards, and code reviews.
• Build intelligent automation to streamline research workflows.
• Collaborate with Product, Research, and Data teams to identify AI-driven value.
• Evaluate emerging technologies to strengthen the platform and practices.

Skills

C# / .NET development

Distributed systems design

RESTful services

Cloud platforms (AWS/Azure)

MSSQL / relational DB

AI/LLMs familiarity

Telemetry & observability

Education

Bachelor's Degree

Tools

SQL Server

Web API

AWS

Azure

Job description

Job Description

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 and are 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 Senior 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, LoopNet, Homes.com and Apartments.com. 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.

Responsibilities

• 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.

Basic Qualifications

• 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.
• MSSQL or other relational database development experience.
• 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.

Preferred Qualifications and Skills

• Strong communication skills (to both business and technical partners).
• 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.

What’s in it for You

When you join CoStar Group, you’ll experience a collaborative and innovative culture working alongside the best and brightest to empower our people and customers to succeed.

We offer you generous compensation and performance-based incentives.

CoStar Group also invests in your professional and academic growth with internal training, and tuition reimbursement.

Benefits

• 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

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.

Equal Employment Opportunity

CoStar Group is an Equal Employment Opportunity Employer; we maintain a drug-free workplace and perform pre-employment substance abuse testing. 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 37 years, giving us the perspective to create truly unique and valuable products and services. We’ve continually refined, transformed and perfected our approach to our business, creating a language that has become standard in our industry and for our customers. 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. CoStar Group is committed to creating a diverse environment and is proud to be an equal opportunity workplace and affirmative action employer. All qualified applicants will receive consideration for employment without regard to race, color, religion, gender, gender identity or expression, sexual orientation, national origin, genetics, disability, age, or veteran status. CoStar Group is also committed to compliance with all fair employment practices regarding citizenship and immigration status. If you are a qualified individual with a disability or a disabled veteran, you may request a reasonable accommodation if you are unable or limited in your ability to use or access www.costargroup.com/careers as a result of your disability. You can request reasonable accommodations by sending an email to [e-mail].