Senior Software Engineer (C#/.NET)

CoStar Group; Virginia (MN); On-site; USD 143,000 - 187,000; Full time

Benefits offered by this job

Healthcare coverage

401(k) matching

Stock purchase plan

Paid time off

Tuition reimbursement

Job summary

CoStar Group is seeking a Senior Software Engineer (C#/.NET) to expand the data platform powering CoStar Suite, LoopNet, Homes.com and Apartments.com. You will build distributed, API-driven systems and design AI-powered solutions to enhance product capabilities.

The role requires deep .NET expertise, cloud experience (AWS/Azure), and data modeling, with a focus on reliability, observability, and scalable architecture. Arlington, VA—in-office Mon-Thu, optional remote Friday.

Qualifications

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

Responsibilities

• Build big, distributed, API-driven systems for tens of thousands of users.
• Design AI-powered software to enhance customer experience and platform intelligence.
• Integrate AI skills, agents, tools, and intelligent workflows into systems.
• Produce robust, scalable code using C#, .NET Framework, SQL Server, AWS.
• Use telemetry to identify anomalies and performance bottlenecks.
• Lead software design, development standards, and code reviews.
• Collaborate with Product, Research and Data teams on AI-driven value.

Skills

API design

Distributed systems

C#/.NET

RESTful services

Data modeling

LLMs

Telemetry

Education

Bachelor's Degree

Tools

AWS

Azure

SQL Server

ASP.NET MVC

Web API

Job description

Senior Software Engineer (C#/.NET)

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.
• Working knowledge and experiencewith cloud-basedplatforms (AWS or Azure).
• Experience with RESTful web servicesand 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).
• SQL and database development knowledge.
• Familiarity withAWSPaaSservices such as Lambda, DynamoDB, andSQS.
• 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.

Our benefits package includes (but is not limited to):

• 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 avariety 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.

#LI-AR

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