Citi★3.9 (21k)· London

Work with Solidity, Web3J/Web3JS/Ethers.js/Viem, Java/Spring, Node.js, and blockchains such as Ethereum, Hyperledger Besu, Canton, and Solana, using Hardhat/Foundry/Truffle for testing. Contribute to Citi's Integrated Digital Assets Platform (CIDAP) building Web3 components for tokenization, smart contracts, and on-chain settlement.

Build backend services in Java/Spring on AWS, working with event-driven systems (Kafka, event sourcing). You’ll join a pre-launch UK fintech building an AI-powered autonomous savings app, contributing to the money-movement engine, ledger, and APIs alongside the CTO.

STINT★3.6 (65)via Jack & Jill· London

Build and maintain core systems using Python (Django), Go, Flutter, GraphQL, PostgreSQL on AWS/EKS with DataDog and GitLab. You’ll join a cross-functional product pod powering Stint’s platform that combines a flexible student workforce with AI for hospitality brands.

Superdrug★3.3 (3k)· London

You'll work with C#, Bootstrap, SQL Server, Xamarin/Flutter, .NET Core, Visual Studio, .NET Framework 4.6+, MVC 5, and Azure DevOps. The team develops and supports business-critical retail applications, including a Stores Intranet and Stock Management/Order & Collect systems.

Lead a 30-engineer team at a UK digital bank, driving adoption of GCP, microservices, containerization (Kubernetes/Docker), and AI/ML APIs. You will build and scale customer-facing digital platforms and cloud-native services using agile and DevOps practices, with exposure to Flutter, Go, and TypeScript. This role focuses on shaping the engineering pillar and scaling capability during the bank's transformation.

You will work with Solidity, React, Node.js, TypeScript, GraphQL, React Native or Flutter, and Ethereum or Binance Smart Chain. This consulting company builds web, mobile, and Web3 applications with blockchain integration.

You will design and maintain cross-platform applications using Flutter and Dart, integrating with REST APIs and backend services. The company develops and enhances a range of digital products, and you will collaborate with Product, Design, QA, and Backend Engineers in a modern engineering environment.

You’ll work in Rust, C, or C++ on the Agave client’s block-production pipeline, designing shared-memory systems and optimizing scheduling, verification, and throughput for the Solana network at a Solana R&D lab.

You'll work with Python, Go, Django, Flutter, AWS, and PostgreSQL on an AI workforce optimisation platform that connects temporary workers with hospitality clients via AI scheduling, scaling from 250,000 to millions of users while transitioning from a monolith to microservices.

Capital on Tap★3.9 (55)· London

You'll design and build scalable solutions using C#, .Net, SQL Server, React, and TypeScript across Capital on Tap's financial platform for small businesses—which includes a business credit card, spend management tools, and savings products serving 200,000+ customers. You'll own problems end-to-end from concept to production, mentor engineers, shape architectural decisions, and work closely with cross-functional teams in a hybrid London role.

Use Kotlin Multiplatform (KMP), Flutter, or React Native; integrate TFLite/CoreML and real-time protocols (WebSockets, SSE). You'll build consumer-facing mobile apps and client SDKs for behavioral AI retail solutions, collaborating with ML engineers and product designers.

You’ll work with Node.js, TypeScript, React, ethers.js, viem, Web3.js, Solana Web3.js, and CI/CD microservices. The FinApps Access team builds the backbone of on-chain access for financial institutions—designing systems that route, protect, and optimize transactions across dozens of EVM and non-EVM blockchain networks.

Capital on Tap★3.9 (55)· London

You'll work with C#, .NET, .NET Core, Flutter, Dart, Riverpod, GoRouter, Kotlin, Swift, SQL Server, MongoDB, Firestore, GCP, Azure, and CodeMagic. You'll own backend services for the Banking and Repayments platform and contribute to iOS and Android mobile development.

You will work with Node.js, TypeScript, C++, MySQL (Aurora), Redis, OpenSearch, AWS (Fargate, Lambda, CloudWatch), Docker, and Terraform. The backend team builds and operates core APIs, real-time collaboration, file storage, and background processing for Rive’s cloud platform, plus full-stack services for the marketplace and customer-facing experiences.

You'll develop and maintain the Agave client for the Solana blockchain using Rust or C++, focusing on performance optimization, security testing, and distributed systems reliability. Anza is an R&D lab building robust blockchain infrastructure and protocols to improve Solana's scalability and security. You'll analyze code, design benchmarking solutions, and collaborate across teams to enhance the network's robustness against emerging threats.

As a Staff Engineer, you'll build APIs, workflow orchestration, and tool integration using Java, Spring Boot, JOOQ, SNS+SQS, Kafka, MySQL, PostgreSQL (RDS/Aurora) on AWS. You'll join the team building Tide's agentic platform to bridge backend systems with Generative AI for SME banking services.

Lead architecture of Tide's agentic platform, working with Java, Spring Boot, JOOQ, Kafka, AWS (RDS, Aurora, EKS), Docker, Terraform, DataDog, and GitHub CI/CD. You'll design shared services (context APIs, tool layers, policy controls, auditability) and build evaluation pipelines for AI reasoning and safety. Tide provides business accounts and administrative solutions for SMEs.

You'll develop Flutter and Dart mobile applications for Gophr, a same-day delivery platform reimagining logistics for businesses, customers, and couriers. The role involves building high-performance, complex apps on scalable cloud infrastructure, implementing performance-focused UI components, and collaborating with product managers and UX designers to deliver an automated last-mile delivery solution. Junior positions require 1+ year Flutter experience; mid-level roles require 2+ years Flutter and 3+ years native iOS/Android development with architectural pattern knowledge.

Jane Street seeks a front-end engineer skilled in web technologies (CSS, DOM, React, Vue, Angular, Flutter) and typed functional programming (Elm, ReasonML, PureScript, TypeScript) to design and build browser-based tools for their trading infrastructure. The role involves creating sophisticated, polished UIs for expert users, developing shared libraries and abstractions, and collaborating across the full stack with traders and end-users to refine development practices.