Senior Developer

We're looking for a talented Senior Developer to help build and evolve our products, services, CLIs and libraries. You'll join an AI-native team, hands-on creating new software and enhancing what we already have, working closely with product engineering, QA and customer support. As a senior figure you'll coach team members, take a leading role in critical projects and contribute to our future technical direction. This is a hands-on technical role rather than a line-management one, though it may grow to include team leadership for the right candidate.

Our work spans two product areas on one shared tech stack: a cloud, microservice-based platform, and a lower-level engine with its command-line tools, libraries and file processing. We're looking for depth in one and the willingness to work across both.

Shared core: C#, .NET, Linux, Git, Azure DevOps.

Cloud platform: Azure, Docker, Kubernetes, Blazor, RabbitMQ, MongoDB, React, REST.

Engine, CLIs and libraries: cross-platform .NET, native interop, file and stream processing, packaging for Linux and Windows.

Responsibilities

• Own the technical direction, architecture and quality of a service or product area: setting performance and scalability targets, identifying technical risks and implementing mitigations, and taking accountability for reliability in production, for cross-cutting design decisions, and for balancing business value against technical improvement.
• Lead the design, development and maintenance of complex software in C#, architecting modular, reusable components with SOLID principles, and designing the public APIs and interfaces that others depend on so they stay robust and backwards compatible, documenting the decisions and rationale behind them.
• Keep existing systems maintainable through refactoring and modernisation, and ensure our software handles untrusted and malformed input safely, with predictable performance and memory behaviour under real workloads, adhering to security best practices and compliance requirements.
• Drive the adoption of test-driven development and testability across the codebase, conduct code reviews, enforce coding standards, maintain CI/CD pipelines for automated build, test and deployment across platforms, and partner with QA on test strategy and coverage.
• Drive effective and responsible adoption of Agentic development across the team, establishing where these tools add value, where human review is non-negotiable, and how quality is maintained as their use grows.
• Lead the diagnosis of complex, cross-system and production issues, and put in place the practices that stop them recurring.
• Mentor junior and mid-level developers, sharing knowledge, running technical training and keeping the team current on emerging technologies.
• Support agile ceremonies, planning and estimation, working with product management and customer support to keep delivery smooth and transparent.

Required Knowledge, experience and values

• Expert-level C# and .NET with significant commercial experience delivering complex, production software, including advanced language features, asynchronous programming, LINQ, multi-threading, concurrency and data storage concepts.
• In-depth knowledge of software architecture and design, applied to complex, maintainable, high-performance systems, and adept at managing and modernising legacy codebases.
• Deep expertise in one of our two product areas, and the willingness to work across both:
  • Cloud and distributed systems: designing and running services on Azure for scalability, resilience and cost-effective operation, with messaging, containerisation and orchestration (Docker, Kubernetes) and web technologies such as Blazor or Web API.
  • Engine, CLI and library development: library and CLI interface design, file and stream processing, performance and memory behaviour on large inputs, and cross-platform builds and packaging.
• Deep commitment to TDD/BDD and test automation, with mastery of frameworks such as NUnit, xUnit or MSTest.
• Working knowledge of secure coding, data protection and common classes of vulnerability.
• Experience setting up and managing CI/CD pipelines, with proficiency in Git and Azure DevOps, and a thorough understanding of the software development life cycle and Agile ways of working.
• Experience applying Agentic development tools in a commercial setting, and a considered view on how to adopt them without compromising quality.
• Strong Linux skills, including building, deploying and troubleshooting .NET software on Linux in production, alongside working knowledge of Windows.
• Experience mentoring developers and conducting code reviews.
• Excellent collaboration and communication skills, and a keen interest in continuous improvement and personal development.

We encourage you to apply even if your experience is not a 100% match with the position.

Beneficial Knowledge, experience, and values

• Native interop from C#, or other low-level and systems-level development experience.
• Microservices architecture and distributed systems, with messaging and NoSQL stores.
• Experience with file formats, binary parsing, or fuzzing and robustness testing against malformed input.
• Full-stack development across frontend and backend.
• Experience with Python or other scripting languages.
• Familiarity with published standards and code-first tools (Markdown, Mermaid, LucidChart).
• Experience with C or C++, for occasional support of our legacy native components.
• Passionate yet pragmatic about software design and architecture.

About Us

We didn’t start out as a traditional security product. In the beginning, Glasswall was one of only two file sanitization filters in the US Intelligence Community’s highly classified networks. We are rated #1 by the National Security Agency. We designed Glasswall CDR to protect businesses against the most advanced file-based threats. Today, we’re trusted by commercial and government organisations around the world.

In June 2025 Glasswall officially entered a new era of growth and innovation having been acquired by the leading private equity firm, PSG Equity. This marks a significant milestone for our company and one that underscores the strength of our business, the dedication of our team, and the exciting potential that lies ahead.

With PSG’s strong track record of scaling high-growth cybersecurity and technology businesses, we are better positioned than ever to accelerate innovation, expand into new markets, and deliver even greater value to our clients, employees, and stakeholders.

Cybersecurity is a mission-critical field, and we’ve always believed that staying ahead means moving faster, continually adapting to meet new challenges and investing more boldly in the future. This partnership empowers us to do exactly that while maintaining the same leadership, values, and commitment to excellence that have brought us this far

We’re excited for what’s to come so now is a great time for you to join us on our journey.

Inclusion

At Glasswall we believe that diversity of people and thought are central to our purpose. We are committed to making Glasswall a company that is attractive to people of many different backgrounds. This includes diversity in every sense of the word: those with different backgrounds, ages, ethnicities, gender identities, sexual orientations, ways of thinking and those with disabilities or neurodivergent conditions. We therefore welcome and encourage applications from everyone, including those from groups that are under-represented in our workforce.

One of our corporate objectives is to ensure that the organisational health of the firm is highly rated by our employees. We believe that this is only possible if we promote a culture of inclusion and respect across our business. Every six months we survey employees on a range of questions relating to our organisational health. This holds a mirror-up to a business and ensures that we can focus on where we need to do better.

We have an Organisational Health Committee, which is chaired by a non-executive position. The panel has been formed to guide the leadership in taking positive action that supports a good work-life balance, family friendly relations and to be inviting to a diverse range of potential employees.

We also have a Women in Technology Group which has been formed to promote balance in the way that we communicate with, promote, encourage, and support people across our business.

Work/Life Balance

Our team puts a high value on work-life balance. It isn’t about how many hours you spend at home or at work; it’s about the flow you establish that brings energy to both parts of your life. We believe striking the right balance between your personal and professional life is critical to lifelong happiness and fulfilment. We offer flexibility in working hours and encourage you to find your own balance between your work and personal lives.

Salary and Benefits

• Glasswall offers a competitive salary and incentives package.
• We offer flexible and remote working options, with hybrid working from our office in the Central London area.
• Office travel and incidental WFH expense coverage.
• 25 days holiday (plus public holidays).
• Private Medical Insurance including mental health support and cancer care.
• Enhanced sick pay.
• Company sponsored life, critical illness, and income protection insurance.
• Contributory pension scheme.
• Access to ‘salary sacrifice’ benefits such as Cycle to Work and Tech Schemes.

A successful candidate will live in the United Kingdom and be comfortable working from home with some meetings being held in the London office.

We are looking for someone with relevant skills and experience, not a checklist that exactly matches the job description. We want to help you grow, and in return, you help us grow into a stronger, more inclusive organisation.

Glasswall is an equal opportunity employer and does not discriminate on the basis of race, national origin, gender, gender identity, sexual orientation, disability, age, or other legally protected status.