Senior Software Engineer (C#/.NET)

CoStar; Arlington (TX); Hybrid; USD 143,000 - 187,000; Full time

Benefits offered by this job

Healthcare coverage

401(k) with matching

Employee stock purchase plan

Tuition reimbursement

On-site fitness center

Job summary

CoStar Group in Arlington, VA, is seeking a Senior Software Engineer for the Platform Development team to build distributed API‑driven systems supporting CoStar's brands. You will design AI‑powered solutions and integrate AI agents, tools, and workflows to enhance product capabilities.

You'll collaborate with Product, Research, and Data teams, apply telemetry and observability, and push for code quality with evidence‑based improvements.

Qualifications

• Bachelor's degree from an accredited university.
• 5 years of deep .NET development (C#) with cross‑platform communication such as Web API.
• Experience with cloud platforms (AWS or Azure).
• Experience with RESTful services and ASP.NET MVC.
• Experience building large‑scale distributed systems in an agile environment.
• Data modeling experience.
• Familiarity with LLMs, prompt engineering, or agent architectures.
• Experience with monitoring, telemetry, observability, or automated diagnostics.

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 robust, efficient, maintainable code using C#, .NET, SQL Server, AWS.
• Utilize telemetry to identify anomalies and performance bottlenecks.
• Lead software design, development standards, and code reviews.
• Collaborate with Product, Research, and Data teams to drive business value.

Skills

C# programming

NET Framework

RESTful APIs

Cloud: AWS/Azure

Data modeling

SQL/SQL Server

LLMs/AI concepts

Observability/Telemetry

Education

Bachelor's Degree in Computer Science or related field

Tools

ASP.NET MVC

Web API

SQL Server

AWS

Azure

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.

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. 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.

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 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).
• 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.

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

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.