Senior React Platform Engineer

Mattermost is the leading collaborative workflow platform for defense, intelligence, security, and critical infrastructure. Trusted by the U.S. Department of War and Fortune 500s, our platform runs on-premises and in private clouds, delivering secure messaging, file sharing, workflow automation, audio/screenshare, and project management—all with full data and operational control. Mattermost powers high‑stakes workflows across mission planning, real‑time, real‑world operations, Dev Sec Ops , incident response, and cyber defense—enabling secure collaboration from tactical edge and DDIL environments to enterprise HQ.

Teams operate across web, desktop, and mobile, with embedded interoperability for Microsoft Teams, Outlook, and Microsoft 365.

Mattermost is looking for a Senior React Platform Engineer to help us redefine the limits of web application performance and reliability. You will join the Core Web team to lead the evolution of our web architecture, shared libraries, and networking strategies. Your work sits at the intersection of modern frontend infrastructure and extreme environment resilience. You’ll be responsible for ensuring that our web platform is both a joy for developers to build on and a reliable tool for users in the most challenging network conditions—specifically DDIL (Disconnected, Denied, Disrupted, Intermittent, and Limited) environments.

This isn’t just about building features; it’s about building the engine that powers them.

• Implement secure communication features and real‑time messaging capabilities optimized for high‑latency or disrupted network conditions.
• Optimize web application performance, including bundle size, initial load time, runtime memory usage, and asset delivery pipelines.
• Design and maintain shared React component libraries and architectural patterns to ensure platform‑wide consistency and scalability.
• Collaborate with backend engineers to integrate web apps with APIs and ensure smooth data synchronization under constrained or intermittent network environments.
• Contribute to Mattermost’s open‑source React codebase, sharing platform‑level and resilience‑focused solutions with the broader developer community.
• Work with product managers and designers to translate user requirements into technical solutions and prototypes, with a focus on graceful degradation and resilience.
• Implement comprehensive testing strategies including unit tests and automated end‑to‑end testing (e.g., Cypress or Playwright) under simulated network stress.
• Participate in code reviews and provide mentorship to colleagues on React best practices, platform standards, and resilient architecture.
• Proactively master and integrate the latest advancements in AI and LLM‑powered development tools (e.g., Cursor, Claude, Git Hub Copilot) to accelerate engineering velocity, automate repetitive platform tasks, and establish best‑in‑class AI‑assisted workflows.

• BS in Computer Science, Computer Engineering, or related field/experience.
• 5+ years of professional experience developing mobile applications with React.
• Proficiency with AI/LLM tools to improve and accelerate development.
• Experience with state management libraries (Redux, Zustand, or similar) and async data handling.
• Familiarity with web app testing frameworks and debugging tools for React applications.
• Strong problem‑solving skills and ability to work independently in a remote, distributed team environment.
• Excellent written and verbal communication skills for collaborating across time zones.
• For candidates residing in the U.S.:
  This role may require the ability to obtain and maintain a U.S. government security clearance in the future. As such, U.S. applicants must be U.S. citizens and eligible under applicable clearance requirements.
• Applicants must meet eligibility requirements for access to export‑controlled information as defined by U.S. export control laws, including EAR and ITAR.

• Previous experience building end‑user products for enterprises or security‑focused users.
• Contributions to open‑source projects.
• Knowledge of accessibility standards and implementing inclusive web experiences.
• Has worked fully remotely with…