Senior Software Engineer

The Portfolio Group; Greater London; On-site; GBP 90,000 - 120,000; Full time

Job summary

The Portfolio Group is seeking a Senior Software Engineer to own the application and integration layer behind AI-powered products. You will work across the full stack, designing services, APIs, and interfaces connecting AI capabilities to the products customers and colleagues use every day.

You'll play a key role in building MCP integrations, agent-to-agent connectivity and robust API services, while also developing responsive, accessible interfaces in React and TypeScript.

Qualifications

• Strong Python experience for backend and integration development.
• Strong TypeScript/JavaScript and React experience building production applications.
• Strong API design experience, including REST/GraphQL, authentication, authorization, versioning and streaming.
• Hands-on MCP or comparable tool/plugin integration technologies, with interest in AI agents.
• Solid experience with AWS services (Lambda, ECS, API Gateway, S3, CloudFront, Cognito, IAM).
• Experience designing and operating distributed or event-driven systems.
• Good understanding of observability, testing and CI/CD.
• Experience with data platforms such as MongoDB, OpenSearch or Databricks.

Responsibilities

• Own the application and integration layer of AI products end to end, including APIs and frontend development.
• Design, build and maintain MCP servers exposing systems to AI agents.
• Develop agent-to-agent connectivity with message contracts, state management and retries.
• Design scalable APIs using REST/GraphQL with authentication, authorization and streaming.
• Build production frontend applications using React, TypeScript and JavaScript.
• Collaborate with UX/product teams to deliver accessible, responsive interfaces.
• Develop AI-specific user experiences with streaming results and source information.
• Integrate with internal and third-party services focusing on security and reliability.
• Establish automated testing across backend and frontend (unit, contract, E2E).
• Work with platform engineering on deployment, observability, logging and runtime readiness.
• Provide architectural guidance and mentoring to other engineers.

Skills

Python backend

TypeScript

React

API design

CI/CD

Observability

Testing

Mentoring

Tools

MCP (Model Context Protocol)

AWS (Lambda, ECS, API Gateway, S3, CloudFront, Cognito, IAM)

MongoDB

OpenSearch

Databricks

REST/GraphQL

WebSockets

Job description

We're looking for a Senior Software Engineer to join a growing AI team and take ownership of the application and integration layer behind a new generation of AI-powered products.

This is a genuinely full-stack engineering role, combining production-grade backend development, API design, AI integrations and frontend engineering. You'll work across the full application lifecycle, designing the services and interfaces that connect AI capabilities to the products customers and colleagues use every day.

You'll play a key role in building MCP integrations, agent-to-agent connectivity and robust API services, while also developing responsive, accessible interfaces in React and TypeScript.

What you'll be doing

• Own the application and integration layer of AI products end to end, covering APIs, integrations, service boundaries and frontend development.
• Design, build and maintain MCP servers that safely expose systems, content and tooling to AI agents.
• Develop agent-to-agent connectivity, including message contracts, state management, retries and failure handling.
• Design clear, scalable APIs using REST and/or GraphQL, including authentication, authorisation, versioning and streaming interfaces such as SSE or WebSockets.
• Build production frontend applications using React, TypeScript and JavaScript.
• Work closely with UX and product teams to turn designs into accessible, responsive and intuitive interfaces.
• Develop AI-specific user experiences including streaming responses, citations, source information, agent/tool progress and graceful error handling.
• Integrate with internal platforms and third-party services, considering security, scalability, performance and reliability.
• Establish automated testing across backend and frontend applications, including unit, contract and end-to-end testing.
• Work with the platform engineering team on deployment, observability, logging, tracing and operational readiness.
• Act as the technical owner for the application and integration layer, making and documenting key architectural decisions.
• Provide technical guidance, code reviews and mentoring to other engineers.

You should have:

• Strong commercial experience with Python for backend and integration development.
• Strong TypeScript/JavaScript and React experience building production applications.
• Strong API design experience, including REST and/or GraphQL, authentication, authorisation, versioning and streaming.
• Hands-on experience with MCP (Model Context Protocol) or comparable tool/plugin integration technologies, alongside an interest in AI agents and agent-to-agent connectivity.
• Solid experience with AWS, ideally including services such as Lambda, ECS, API Gateway, S3, CloudFront, Cognito and IAM.
• Experience designing and operating distributed or event-driven systems.
• A strong understanding of observability, testing and CI/CD practices.
• Experience working with data platforms or stores such as MongoDB, OpenSearch or Databricks.
• Experience integrating internal systems and third-party services securely and reliably.
• Experience working closely with designers to deliver production-quality frontend applications.
• A good understanding of accessibility and frontend performance.
• Experience with RAG, AI agents, tool use or other generative AI application patterns would be advantageous, although deep ML expertise isn't required.

This is an opportunity to have genuine ownership over how AI capabilities become usable, scalable software products.

You'll be joining an AI-focused engineering environment where you can work at the intersection of software engineering, APIs, cloud infrastructure and generative AI, while helping establish the engineering standards and architecture that will support future products.

If you're a senior engineer who enjoys moving between backend architecture and frontend delivery, wants ownership rather than simply a list of tickets, and is excited about where AI agents and modern application architecture are heading, we'd love to hear from you.