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Agent guide: [/agents.md](https://www.wearedevelopers.com/agents.md). --- # Software Engineer - Web App & DevEx - **Company:** Número De - **Location:** Madrid, Spain (Remote available) - **Contract:** Permanent contract - **Skills:** Clean Code Principles, PHP (Programming Language), Application Programming Interfaces (APIs), Software Quality, Computer Programming, Customer Data Management, Distributed Systems, Symfony, Web Applications, Web Platforms, Web Services, WebSocket, AI Infrastructure, Backend, Stripe, Front End Software Development, Api Design, Doctrine (orm) - **Published:** September 3, 2026 - **Apply:** https://www.adzuna.es/contact-us.html ## About the Role + Strong experience building backend systems and APIs + Strong programming experience in one or more backend languages, with the ability to quickly learn and work effectively in new languages and technologies + Experience building reliable, maintainable and well-tested production systems + Good understanding of API design, asynchronous workloads and distributed systems concepts + Strong engineering fundamentals around security, reliability and performance + Strong communication and collaboration skills, with the ability to work effectively across engineering, Product and Design + Strong ownership and autonomy, with good judgement around when to involve others + Comfortable using AI-assisted development tools and agents to improve productivity, while understanding their limitations and maintaining responsibility for the quality, security and correctness of the resulting code Nice to have + Experience with PHP, Symfony and/or Doctrine + Experience with WebSockets + Experience building public APIs or other developer-facing products + Experience with usage-based billing, credits or financial data + Experience contributing to architectural decisions and mentoring other engineers ## Description We're looking for a Senior Software Engineer to help build and evolve the systems and APIs that power Runware's Web App and Developer Experience (DevEx). You'll work closely with backend engineers, frontend engineers, Product, Design and other teams to build reliable internal and developer-facing APIs and functionality that make complex AI infrastructure simple to use. You'll take ownership of backend work from understanding requirements and technical constraints through to implementation and delivery, contributing to the quality, reliability and evolution of the Web App and its supporting APIs. This role combines technical depth with product thinking and collaboration. You'll be expected to work autonomously, contribute to technical decisions and help turn ambitious ideas into robust production systems. What you'll do + Build and maintain internal and developer-facing APIs and services that power the Web App and developer experience + Develop and evolve public API functionality, including task types, validation, routing and WebSocket/REST behaviour + Own and maintain the Admin API and panel as an internal platform used across Runware + Work with usage, billing and customer data to ensure accuracy and reliability, including Stripe + Investigate and resolve production issues and security vulnerabilities affecting the Web App and its APIs + Write, test and review clean, maintainable code, contributing to strong engineering practices and code quality + Work with Product, Design and engineering teams to clarify requirements, identify dependencies and define well-scoped technical solutions + Contribute to technical decisions, work across frontend and backend boundaries where appropriate, and collaborate with the wider Backend team where specialist knowledge or shared systems are involved ## Related Videos - [Coffee with Developers](https://www.wearedevelopers.com/videos/354-coffee-with-developers) - [Navigating Growth, Scaling Challenges, and Office Expansions with David Singleton, CTO at Stripe](https://www.wearedevelopers.com/videos/100362-navigating-growth-scaling-challenges-and-office-expansions-with-david-singleton-cto-at-stripe) - [Profiling Symfony & PHP apps with Blackfire](https://www.wearedevelopers.com/videos/265-profiling-symfony-php-apps-with-blackfire) - [Developing the Backend with Stefan Lingler, CTO at Shpock](https://www.wearedevelopers.com/videos/100360-developing-the-backend-with-stefan-lingler-cto-at-shpock) - [Throwing off the burdens of scale in engineering](https://www.wearedevelopers.com/videos/608-throwing-off-the-burdens-of-scale-in-engineering) - [Meet Your New BFF: Backend to Frontend without the Duct Tape](https://www.wearedevelopers.com/videos/682-meet-your-new-bff-backend-to-frontend-without-the-duct-tape) ## Related Articles - [Fully Remote Software Engineer Jobs](https://www.wearedevelopers.com/magazine/447-fully-remote-software-engineer-jobs) - [Is Software Engineering Over-Saturated?](https://www.wearedevelopers.com/magazine/418-is-software-engineering-over-saturated) - [The 12 Best Jobs for Software Engineers](https://www.wearedevelopers.com/magazine/401-the-12-best-jobs-for-software-engineers) - [Top-Paying Tech Jobs (with Salaries)](https://www.wearedevelopers.com/magazine/372-top-paying-tech-jobs-with-salaries) - [Find a Developer Job: 12 Best Job Sites For Developers](https://www.wearedevelopers.com/magazine/165-find-a-developer-job-12-best-job-sites-for-developers) - [Why Upskilling And Reskilling is Important For Developers](https://www.wearedevelopers.com/magazine/428-why-upskilling-and-reskilling-is-important-for-developers)