Senior Software Engineer (C#/.NET)

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

Benefits offered by this job

Healthcare coverage

401(k) matching

Employee Stock Purchase Plan

Paid time off

On-site fitness

Job summary

CoStar Group in Arlington, VA seeks a Senior Software Engineer (C#/.NET) to build large distributed, API-driven systems for tens of thousands of users. You will design AI-powered solutions, integrate AI agents and workflows, and ensure robust code using C#, .NET, SQL Server, and AWS.

Responsibilities include telemetry, observability, and diagnostics to improve reliability, plus collaboration with Product, Research, and Data teams to create business value with AI-driven automation.

Qualifications

• 5+ years of deep .NET (C#) development experience, including Web API.
• Experience with cloud platforms (AWS or Azure).
• Experience with RESTful web services and ASP.NET MVC.
• Experience architecting, designing, and building large-scale distributed, service-oriented systems in an agile environment.
• Data modeling experience and data governance concepts.
• Familiarity with LLMs, prompt engineering, or agent-based architectures.
• Experience with monitoring, telemetry, observability, or automated diagnostics platforms.
• Strong communication skills with business and technical partners.

Responsibilities

• Build large, 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 into internal and customer-facing apps.
• Produce robust, maintainable code using C#, .NET Framework, SQL Server, and AWS.
• Use AI models to enhance monitoring, observability, and diagnostics.
• Implement telemetry-driven solutions to identify anomalies and performance bottlenecks.
• Lead software design, development standards, and code reviews.
• Build intelligent automation to streamline research workflows and improve efficiency.
• Collaborate with Product, Research, and Data teams to identify AI-driven value opportunities.
• Continuously evaluate emerging technologies to strengthen our platform.

Skills

.NET/C# development

RESTful web services

ASP.NET MVC

Cloud platforms (AWS/Azure)

LLMs / prompt engineering

Telemetry/observability

Data governance & quality

Distributed service-oriented arch

Education

Bachelor’s degree

Tools

SQL Server

Job description

Senior Software Engineer (C#/.NET)

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

Overview

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.

Responsibilities

• 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.

Basic Qualifications

• 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.

Preferred Qualifications and Skills

• 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.

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 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.

Legal Statements

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

CoStar Group is also committed to creating a diverse environment and is proud to be an 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.

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].

Visa Sponsorship: CoStar Group is not able to provide visa sponsorship for this position.