Senior Agentic Software Engineer

AI-native engineering | Global cybersecurity startup Location: Shenfield, Essex (in office). No visa sponsorship available. Salary: £50,000 to £90,000, depending on experience. The opportunity We are hiring an exceptional Senior Software Engineer to join a fast-growing global cybersecurity startup. This is a senior, hands-on role for someone who can take a difficult problem, make sense of it quickly, decide what needs to happen and deliver a working result. You will not receive a queue of perfectly defined tasks. You will be trusted to investigate unfamiliar systems, challenge assumptions, make sound decisions and own important parts of the product. We are looking for someone with strong engineering experience, expert-level AI capability and the cognitive agility to solve new problems under pressure. This is a full-time, in-office role based at our Shenfield, Essex office. Unfortunately, we are unable to offer visa sponsorship for this role, so applicants must already have the right to work in the UK. Please note you will have to demonstrate the use of a full agentic stack already and demonstrate advanced interest and aptitude in all of the modern AI programming capabilities. This is not just about using ChatGPT. This is about being a full agentic developer. You will be working directly with the CTO and the CEO. This is very much a hands-on product-agentic engineering opportunity. What makes this role different > You must be an expert with AI. AI is central to how we build software. It is not an occasional productivity tool. You should already be highly skilled with AI coding agents and tools such as Claude Code, GitHub Copilot, ChatGPT or equivalent platforms. You must be able to use AI to: Understand unfamiliar codebases quicklyInvestigate faults and production incidentsDesign and compare technical approachesBuild and improve production-quality codeCreate meaningful automated testsReview, debug and refactor existing systemsAutomate repetitive engineering workRun several lines of investigation efficientlyIncrease delivery speed without lowering quality You remain accountable for everything you produce. You must understand the code, verify the output, test the result and recognise when an AI-generated answer is wrong. The strongest candidate will treat AI as an engineering capability they have mastered, not a shortcut they are experimenting with. You'll have an unlimited budget for AI tools, so you can use the best agents and models available without having to justify every subscription. > You must demonstrate fluid cognitive ability Seniority here is measured by how well you think, not only by how many years you have worked. Our interview process will include practical exercises designed to assess fluid cognitive ability. This means your ability to: Understand unfamiliar problemsIdentify patterns and important detailsSeparate evidence from assumptionsLearn and apply new informationReason clearly with incomplete informationAdapt when the problem changesExplain complex decisions simplyReach sensible conclusions under time pressure These exercises will focus on your reasoning and approach. They will not depend on memorising obscure syntax or performing artificial puzzle tricks. > You must be highly agentic We need someone who creates momentum. A highly agentic engineer does not wait for every step to be assigned. They find the missing information, speak to the right people, use the available tools and move the work towards a result. You will be expected to: Take ownership without needing constant supervisionTurn unclear requirements into an actionable planInvestigate before asking others to solve the problemMake sensible decisions when information is incompleteRaise risks early and propose solutionsFollow work through development, testing and deploymentCheck that the change worked in the real environmentTake responsibility when something goes wrongShare knowledge so the team becomes stronger Independence does not mean working alone. You must communicate clearly, ask focused questions and collaborate well. The difference is that you use collaboration to move the work forward, not to pass ownership elsewhere. What you will do You will own features and engineering initiatives across their complete lifecycle: Understand the customer, business and technical problem.Investigate the current implementation and supporting data.Identify dependencies, security concerns and potential impact.Design a practical technical approach.Communicate the approach clearly.Build the solution.Write appropriate automated tests.Review AI-generated and human-written code critically.Perform impact analysis and regression testing.Deploy and verify the change.Investigate any problems after release.Measure whether the work achieved the intended result. You will also become the technical owner of one or more product areas. This means understanding how they work end to end, maintaining their quality and becoming the engineer others trust for informed decisions. Production and cloud engineering You will help operate the systems you build. Depending on the product area, your work may include: AWS cloud servicesServerless applicationsCI/CD pipelinesPostgreSQL databasesContainers and KubernetesMonitoring, logging and alertingInfrastructure configurationApplication and cloud securityProduction troubleshootingPerformance and reliability improvements Cybersecurity customers depend on our products. Secure engineering, careful testing and production ownership are part of the job. Technology Our products use modern Microsoft, web and cloud technologies, including: C#, .NET and ASP.NET CoreREST APIs and distributed systemsEntity Framework CorePostgreSQLAWS and LambdaServerless architecturesDocker and KubernetesVue.js and modern frontend technologiesGit and GitHubCI/CD and DevOps toolingAutomated testingApplication monitoring and loggingAI coding agents and development tools You do not need prior experience with every item. You must have strong engineering foundations and be able to learn unfamiliar technology quickly. What we are looking for Around 8 to 9 years of relevant software engineering experienceStrong commercial experience building and supporting production softwareExpert-level use of modern AI engineering toolsExcellent problem-solving and fluid reasoning abilityA record of owning complex work from problem to productionStrong C# and .NET experience, or comparable backend expertiseExperience with cloud-based and distributed systemsSound knowledge of databases, APIs, testing and source controlGood judgement about security, maintainability and operational riskClear written and verbal communicationThe confidence to make decisions and the humility to change them when the evidence changes Years of experience alone will not secure this role. We are looking for evidence of judgement, learning speed, ownership and delivery. About the company You will work with an ambitious, fast-growing global cybersecurity startup serving customers across international markets. Our mission is to demystify cybersecurity for SMBs, MSPs and enterprises. We reduce the cost and complexity of cybersecurity by building useful products quickly, shipping them and improving them through real customer feedback. The pace is high. Problems are not always tidy. For the right engineer, that means meaningful ownership, direct influence and the chance to help shape both the product and the engineering culture. Interview process The selection process is designed to test how you work, not how well you rehearse answers. It may include: A discussion about systems you have personally built and ownedA practical AI-assisted engineering exerciseAn unfamiliar problem that tests fluid cognitive abilityCode investigation, debugging or solution-design workA conversation about judgement, ownership and production responsibility We want to see how you gather evidence, use AI, test assumptions, communicate decisions and turn an unclear problem into a dependable result. The standard This is a top-level senior engineering appointment. We are looking for someone who combines deep technical ability with AI expertise, cognitive agility and exceptional personal ownership. If you need every task fully specified before you begin, this role is unlikely to suit you. If you enjoy difficult problems, learn quickly, use AI with real skill and take pride in owning the result, we would like to hear from you. How to apply To apply, please email liz@roboshadow.com. We may miss applications sent through LinkedIn, so email is the best way to make sure yours reaches us.