Senior Software Engineer I

Our software engineers develop the next-generation technologies that change how billions of users connect, explore, and interact with their finances. Our products need to handle data at a massive scale. You'll work alongside the best and the brightest engineering talent in the industry. As a core participant of your team, you'll estimate engineering efforts, design your changes, implement and test your changes, push to live, and triage production issues. You need to be dynamic, collaborative, and curious as we build new experiences, improve existing products, and develop distributed systems powering the world to be financially strong.

This role is on the Experiences team, which builds MX's personal financial management (PFM) products: a money management dashboard, embeddable budgeting, spending, and cash flow widgets, and a personalized insights feed that financial institutions embed in their digital banking apps.

We're looking for a full-stack engineer, equally at home in React/TypeScript and the backend services behind it, who is well versed in applied AI. You'll ship LLM-powered features that make financial data easier to understand, safely and with sensitive data in mind, and help raise how the team uses AI tools to build and operate software.

We need our engineers to be versatile, display leadership qualities and be enthusiastic to take on new problems across the full-stack as we continue to push technology forward.

With your technical expertise you will manage project priorities, deadlines, and deliverables. You will design, develop, test, deploy, maintain, and enhance software solutions.

• Write product or system development code.
• Participate in, or lead design reviews with peers and stakeholders to decide amongst available technologies.
• Review code developed by other developers and provide feedback to ensure best practices (e.g., style guidelines, checking code in, accuracy, testability, and efficiency).
• Enforce clean code and excellent coding practices by conducting thoughtful code reviews.
• Help us build and maintain a world-class technology system so we can achieve our mission of making the world financially strong.
• Collaborate closely with Product Managers to meet and exceed customer needs in the simplest possible ways.
• Contribute to existing documentation or educational content and adapt content based on product/program updates and user feedback.
• Triage product or system issues and debug/track/resolve by analyzing the sources of issues and the impact on hardware, network, or service operations and quality.
• Actively participate in system architecture discussions and technical design reviews to ensure scalability, reliability, and security.
• You will lead by example, and elevate the design, implementation, quality, and strong engineering practices across the team.
• Drive projects and initiatives to implement high quality systems and products.
• Influence, coach, and support engineers on the team, with a strong focus on feedback and growth.

On the Experiences team, you will also:

• Deliver features end to end across our embeddable React widgets, our shared TypeScript widget library, and the backend APIs and services that power them.
• Contribute to an active platform modernization: moving the dashboard's data layer from a legacy Ruby on Rails API to a new TypeScript API service, and moving older front ends to our current React, TypeScript, and design-system stack.
• Design, build, and operate LLM-powered product features, such as plain-language explanations of spending and insights, or assistants that answer questions about a user's own financial data. This includes prompt and context design, retrieval, tool calling, evaluation, and production monitoring.
• Apply privacy and security guardrails when LLMs touch financial data: data minimization, PII redaction, access scoping, output validation, and audit logging, in partnership with Security and Compliance.
• Make informed tradeoffs between model quality, latency, and cost, and choose when an LLM is the right tool and when a deterministic solution is better.
• Use and improve AI-assisted development workflows (coding agents, AI code review, repository context files for agents), and help teammates adopt them effectively and verify AI-generated output.
• Build and maintain automated test coverage (unit, integration, contract, and end-to-end) and the observability needed to operate customer-facing services.

• Bachelor's Degree or equivalent experience.
• 5+ years of experience with software development in one or more programming languages
• 3+ years of experience testing, maintaining, or launching software products
• Professional full-stack experience: production React with TypeScript on the front end, plus building and operating backend services or APIs in at least one server-side language (for example Ruby on Rails or TypeScript on Node.js).
• Experience designing and consuming APIs (REST, RPC, or message-based), and working with caching, background jobs, and asynchronous or event-driven systems.
• Hands-on experience shipping at least one feature or internal tool built on a large language model API

• Retrieval-augmented generation, agent or tool-use architectures, or protocols for exposing tools and data to models (for example MCP).
• Building LLM evaluation harnesses, regression suites for prompts, or guardrail layers; monitoring LLM cost, latency, and quality in production.
• Experience with managed model platforms on a major cloud provider (for example Vertex AI, Bedrock, or Azure OpenAI).
• Front-end stack: React 18/19, MobX or Redux, Material UI, Vite, Vitest, Playwright, Storybook, and contributing to a shared component library or design system.
• Backend stack: Ruby on Rails (including JRuby) with Sidekiq, TypeScript services on Bun or Node.js (for example Hono), Elixir/Phoenix, PostgreSQL, Redis, NATS or RabbitMQ, and protobuf-based RPC.
• Kubernetes, Docker, CI/CD pipelines, and observability tooling such as Datadog or OpenTelemetry.
• Fintech, banking, or other regulated-data domain experience.