21 senior api developer jobs found

Senior .NET / Full Stack Developer – Hybrid – £600/day Outside IR35 | C# | Azure | Event-Driven Systems | Payments | API-Driven We have a unique opportunity for a Senior .NET / Full Stack Developer to join a payments company. As a Senior .NET / Full Stack Developer , you’ll play a key role in building and scaling a high-throughput payments platform as the business enters its next phase of growth. This includes launching new products, enabling new partner integrations, and expanding a platform that already powers multiple live financial services products used globally. You’ll be building on top of a modern, cloud-native platform built with .NET and Azure , designed around API-first architecture and event-driven microservices . The platform supports complex payment flows, partner integrations, and high-volume transaction processing. This is a hands-on senior engineering role where you’ll contribute to architectural discussions, drive engineering best...

Company Description For over 28 years, Version 1 has partnered with leading global brands to deliver digital, cloud, and enterprise application solutions that drive business success. We are proud to be recognised as: Oracle Innovation Partner of the Year 2023 (EMEA) Microsoft Global Partner of the Year (Modernising Applications) AWS Collaboration Partner of the Year (EMEA) One of the Best Workplaces for Women in the UK & Ireland (2023) With 3,700+ people and revenues exceeding €347m/£302m , Version 1 is a market leader in Oracle, Microsoft, and AWS consulting services – and one of the fastest-growing digital consultancies in Europe. Job Description Senior Oracle Fusion Technical Consultant (Cloud Extension Focussed) (Outside IR35 Contract) You must be eligible for CTC Clearance. To be eligible for CTC clearance you need to have lived in the UK for the last 3 years. You must be immediately available or on a very short notice period. Build....

Senior Software Engineer - Golang - Go - Product - TDD – paying up to £550 (Outside IR35) – Hybrid – 3 months We’re a mission-driven tech company that builds products to help people make confident decisions about their finances and everyday services. They are looking for a strong Go Developer who is excited about working with new technologies. Essential Skills: Strong commercial experience with Golang Must have a Product first mentality Experience with observability would be great Experience configuring, deploying, and monitoring applications on AWS. TDD (Test-Driven Development) experience. API build experience is essential, especially with 3rd party API's Comfortable working with relational and NoSQL databases, including complex queries and performance optimization. Solid understanding of web design patterns, including SOLID principles. Experience working in an agile, collaborative environment. Familiarity with automated testing and CI/CD pipelines....

Azure Engineer / Architect 6 month contract London - Hybrid £500 - £650 DOE - Outside IR35 We have multiple opportunities available for Azure Engineers / Architects to join a UK based consultancy who are delivering large digital transformation initiatives across multi-cloud environments. This is a 6 month engagement with potential for further extension. Azure API Platform Engineer Senior platform engineer to lead a multi-cloud API ecosystem, designing secure, scalable microservices and modernising legacy integrations. Also responsible for standardising architecture, improving observability, and driving best practices across teams. Must have: Strong experience with API gateway technologies Deep understanding of Kubernetes in Azure environments Integration between cloud native and legacy systems Azure Cloud Platform & SRE Engineer / Architect Senior engineer to evolve Azure cloud foundations, ensuring secure,...

Mid-Level .NET / Full Stack Developer – Hybrid – £450/day Outside IR35 | C# | Azure | Event-Driven Systems | Payments | API-Driven We have a great opportunity for a Mid-Level .NET / Full Stack Developer to join a growing payments company. As a .NET Developer , you’ll be working as part of an experienced engineering team building and scaling a high-throughput payments platform. The business is entering its next phase of growth, launching new products, enabling new partner integrations, and expanding a platform that already powers multiple live financial services products used globally. You’ll be contributing to a modern, cloud-native platform built with .NET and Azure , designed around API-first architecture and event-driven microservices . The platform supports complex payment flows, partner integrations, and high-volume transaction processing. This is a hands-on development role where you’ll work closely with senior engineers to deliver reliable, scalable...

Senior AI Engineer | £600/day Outside IR35 | 6-Month Contract Industry: Technology / Capital Markets Location: London - 3 days in office Job Type: Contract Our client, a forward-thinking technology organisation, is seeking a Senior AI Engineer to join a team building production-grade AI systems powered by large language models (LLMs). You will work closely with software engineers and product stakeholders to design, develop, and deploy scalable AI applications, focusing on multi-agent orchestration, intelligent tool integration, and reliable production workflows. Responsibilities Design and implement LLM-powered AI systems, including RAG pipelines, vector/knowledge databases, and agentic frameworks. Build and maintain production-grade AI applications with clean code, APIs, data pipelines, and robust error handling. Develop and maintain evaluation frameworks to measure and monitor system performance, accuracy, and reliability. Implement feedback loops...

Contract Java Developer – Data Up to £700 per day Outside IR35 (6 month rolling) In office – City of London Quant Capital is hiring for a small, high-performing market maker in London. This is a junior-to-mid role focused primarily on Java development, with a secondary responsibility owning straightforward Python ETL/data ingestion into AWS and PostgreSQL. This is a growing team focused on data ingestion and building tooling for the wider firm. What you’ll do: Build and enhance Java backend services (APIs, batch jobs, integrations) used across the business Write clean, testable code with solid engineering discipline (testing, code review, debugging, production support) Maintain and extend Python-based ingestion/ETL (pragmatic plumbing, not heavy data engineering) Work with PostgreSQL (schemas, migrations, performant queries, data validation) Improve service reliability: monitoring/logging, sensible alerting, and predictable deployments via CI/CD Tech:...

React Developer Remote with very occasional client visits £400pd to £420pd - Outside IR35 3 - 6 month contract Our client, an established and successful Consultancy are looking for a number of mid-level Developers to join them on a contract basis With head offices in the north of the UK and branches spreading across the globe, they're a dynamic technology consultancy leader with a dedicated team of professionals, partnering with sector leaders After recently winning a large public sector project they are creating a whole new team and need people who are able to start no later than March 16th. This is a fully hands on role where you will work as part of an established successful team, primarily working with React and Typescript technologies We are looking for: Expert knowledge of React Strong proficiency in JavaScript (ES6+), HTML5, CSS3, and responsive UI engineering. Experience with Redux or other state management libraries. Strong understanding of Front End...

IT Applications Manager - Central London £650 - £700 p/d (outside IR35) - 3 month initial term Well-established and highly profitable construction engineering business is seeking an experienced IT Applications Manager to join them on a permanent basis. This is a critical leadership role within an organisation undergoing significant digital transformation, with ambitious growth and acquisition plans driving demand for scalable, standardised and efficient business applications. Reporting into the Head of IT, you will lead the delivery, governance and optimisation of business applications across the enterprise. This role blends strategic oversight, hands-on expertise with modern low-code/no-code platforms and direct leadership of a multidisciplinary applications team. The IT Applications Manager will oversee a suite of core enterprise systems, including but not limited to: Workday, UKG (Kronos), COINS, SharePoint, Snowflake, Autodesk Construction Cloud, Pro-Sapien, Primavera P6...

Lead Java Engineer (Quarkus) Duration: Initial 3 months (with potential extension - project dependent) Location: Remote/London (Hybrid) Onsite requirements: Hybrid - primarily remote with on-site attendance in London for key meetings Engagement Type: Outside IR35 Day Rate: Competitive day rate Right to Work: Candidates must have the legal right to work in the UK. Sponsorship is not available for this position. BPSS screening will be required due to the regulated financial services environment. About Atrium Global Atrium Global is supporting a client of ours within the Banking industry who are delivering a large-scale data platform modernisation programme. Job Overview We are looking for an experienced Lead Java Engineer to join a high-profile engineering programme focused on modernising enterprise data platforms and batch processing capabilities. The role will focus on building and optimising cloud-native Java microservices using Quarkus while integrating with IBM Tivoli...

Contract Java Developer – Data Up to £700 per day Outside IR35 (6 month rolling) In office – City of London Quant Capital is hiring for a small, high-performing market maker in London. This is a junior-to-mid role focused primarily on Java development, with a secondary responsibility owning straightforward Python ETL/data ingestion into AWS and PostgreSQL. This is a growing team focused on data ingestion and building tooling for the wider firm. What you’ll do: Build and enhance Java backend services (APIs, batch jobs, integrations) used across the business Write clean, testable code with solid engineering discipline (testing, code review, debugging, production support) Maintain and extend Python-based ingestion/ETL (pragmatic plumbing, not heavy data engineering) Work with PostgreSQL (schemas, migrations, performant queries, data validation) Improve service reliability: monitoring/logging, sensible alerting, and predictable deployments via CI/CD Tech:...

Overview We are seeking a Senior Python Developer to support a large-scale digital transformation programme. The role focuses on building reliable Back End services, improving system performance, and contributing to a modern, scalable engineering environment. The client is open to strong EU-based talent. Role Detail: Contract Length: 3-6 months Rate: £250-400/day Outside IR35 (Depending on experience) Work Model: Fully Remote Key Skills and Experience Strong commercial experience with Python (Django) Solid understanding of REST APIs , microservices, and Back End architecture. Experience with cloud environments (AWS & Azure). Familiarity with CI/CD pipelines and modern DevOps practices. Strong understanding of relational and/or PostgreSQL. Ability to work in distributed teams and communicate clearly. Experience with Typescript and Svelte Good problem-solving skills and attention to detail. Nice to Have Experience with containerisation (Docker,...

Java Developer - SC Cleared Location: London (1–2 days onsite per month) Contract: Outside IR35 Rate: £600–£675 per day Duration: 12 Month Contract Start: Immediate / Short Notice Preferred Eligibility: Active SC Clearance required (DV clearance ideally) Overview An experienced Java Developer is required to build and maintain scalable, high-performance applications within a secure public sector environment. Requirements Strong experience with Java & Springboot Solid Java back-end development experience Experience working in public sector Strong understanding of API integration and system design Active SC Clearance required (DV clearance ideally)

Full Stack Developer (React / TypeScript / Java) Location: London (1–2 days onsite per month) Contract: Outside IR35 Rate: £650–£700 per day Duration: 12 Month Contract Start: Immediate / Short Notice Preferred Eligibility: Active SC Clearance required (DV clearance ideally) Overview An experienced Full Stack Developer is required to build and maintain scalable, high-performance applications within a secure public sector environment. The role requires a 50/50 split across front-end and back-end development . Requirements Strong experience with React and TypeScript Solid Java back-end development experience Experience working in a full stack capacity (approx. 50/50 front-end/back-end) Strong understanding of API integration and system design Active SC Clearance required (DV clearance ideally)

Lead .NET/Full Stack Developer - Hybrid - £700/day Outside IR35 | C# | Azure | Event Driven Systems | Payments | API Driven We have a unique opportunity for a Lead .NET/Full Stack Developer to join a payments company. As the Lead .NET/Full Stack Developer , you’ll play a key role in shaping and scaling a high-throughput payments platform as the business enters its next phase of growth. This includes launching new products, enabling new partner integrations, and expanding a platform that already powers multiple live financial services products used globally. You’ll be building on top of a modern, cloud-native platform built with .NET and Azure , designed around API-first architecture and event-driven microservices . The platform supports complex payment flows, partner integrations, and high-volume transaction processing. This is a hands-on technical role where you’ll help drive engineering best practices, contribute to architectural decisions, and mentor...

Java Developer - SC Cleared Location: London (1-2 days onsite per month) Contract: Outside IR35 Rate: £600-£675 per day Duration: 12 Month Contract Start: Immediate/Short Notice Preferred Eligibility: Active SC Clearance required (DV clearance ideally) Overview An experienced Java Developer is required to build and maintain scalable, high-performance applications within a secure public sector environment. Requirements Strong experience with Java & Springboot Solid Java Back End development experience Experience working in public sector Strong understanding of API integration and system design Active SC Clearance required (DV clearance ideally)

Full Stack Developer (React/TypeScript/Java) Location: London (1-2 days onsite per month) Contract: Outside IR35 Rate: £650-£700 per day Duration: 12 Month Contract Start: Immediate/Short Notice Preferred Eligibility: Active SC Clearance required (DV clearance ideally) Overview An experienced Full Stack Developer is required to build and maintain scalable, high-performance applications within a secure public sector environment. The role requires a 50/50 split across Front End and Back End development . Requirements Strong experience with React and TypeScript Solid Java Back End development experience Experience working in a full stack capacity (approx. 50/50 Front End/Back End) Strong understanding of API integration and system design Active SC Clearance required (DV clearance ideally)

IT Applications Manager - Central London £650 - £700 p/d (outside IR35) - 3 month initial term Well-established and highly profitable construction engineering business is seeking an experienced IT Applications Manager to join them on a permanent basis. This is a critical leadership role within an organisation undergoing significant digital transformation, with ambitious growth and acquisition plans driving demand for scalable, standardised and efficient business applications. Reporting into the Head of IT, you will lead the delivery, governance and optimisation of business applications across the enterprise. This role blends strategic oversight, hands-on expertise with modern low-code/no-code platforms and direct leadership of a multidisciplinary applications team. The IT Applications Manager will oversee a suite of core enterprise systems, including but not limited to: Workday, UKG (Kronos), COINS, SharePoint, Snowflake, Autodesk Construction Cloud, Pro-Sapien,...

IT Applications Manager - Central London (hybrid) £650 - £700 p/d (outside IR35) 3 month initial term, likely to extend Well-established and highly profitable construction engineering business is seeking an experienced IT Applications Manager to join them on a permanent basis. This is a critical leadership role within an organisation undergoing significant digital transformation, with ambitious growth and acquisition plans driving demand for scalable, standardised and efficient business applications. Reporting into the Head of IT, you will lead the delivery, governance and optimisation of business applications across the enterprise. This role blends strategic oversight, hands-on expertise with modern low-code/no-code platforms and direct leadership of a multidisciplinary applications team. The IT Applications Manager will oversee a suite of core enterprise systems, including but not limited to: Workday, UKG (Kronos), COINS, SharePoint, Snowflake, Autodesk...

IT Applications Manager - Central London £650 - £700 p/d (outside IR35) - 3 month initial term Well-established and highly profitable construction engineering business is seeking an experienced IT Applications Manager to join them on a permanent basis. This is a critical leadership role within an organisation undergoing significant digital transformation, with ambitious growth and acquisition plans driving demand for scalable, standardised and efficient business applications. Reporting into the Head of IT, you will lead the delivery, governance and optimisation of business applications across the enterprise. This role blends strategic oversight, hands-on expertise with modern low-code/no-code platforms and direct leadership of a multidisciplinary applications team. The IT Applications Manager will oversee a suite of core enterprise systems, including but not limited to: Workday, UKG (Kronos), COINS, SharePoint, Snowflake, Autodesk Construction Cloud, Pro-Sapien, Primavera P6...