Software Engineer I (C#/.NET)

CoStar; Arlington (VA); On-site; USD 108,000 - 154,000; Full time

Benefits offered by this job

Healthcare coverage

401(k) retirement plan

Employee stock purchase plan

Paid time off

Job summary

CoStar Group in Arlington, VA is seeking a Software Engineer I to develop distributed API-driven services using C# and .NET. You will design, implement, and maintain AI-enabled features and data integrations across our real estate platforms.

Work with AWS, SQL Server, and modern tooling to deliver reliable software; participate in code reviews, telemetry, and ongoing performance tuning while growing your skills in a collaborative, fast-paced environment.

Qualifications

• Bachelor’s Degree from an accredited, in-person university or college.
• 3+ years of deep .NET development (C#) including cross-platform communication technologies such as Web API.
• Working knowledge of cloud platforms (AWS or Azure).
• Experience with RESTful web services.
• Experience in architecting, designing, and building 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 and data governance concepts.

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 into internal systems and customer apps.
• Produce robust, maintainable code using C#, .NET Framework, SQL Server, AWS, Claude Code.
• Leverage AI models to improve monitoring, observability, diagnostics, and reliability.

Skills

C#/.NET

Distributed systems

RESTful APIs

AI concepts & LLMs

Telemetry & observability

Education

Bachelor’s Degree

Tools

AWS

Azure

SQL Server

Job description

Software Engineer I (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.

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, Claude Code.
• 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.
• Learn software design, development standards, and take part in code reviews.
• Build intelligent automation solutions that streamline research workflows, improve information discovery, and increase operational efficiency across business functions.
• 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.
• 3+ 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.
• Experience in architecting, designing, and building 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.

• 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 a variety of factors, including but not limited to, geographic location, skills, and competencies.

Base Compensation: $108,000 - $154,000 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