Senior Software Engineer - Platform, API

About this role

Senior Software Engineer - Platform, API

Full-time · Engineering · San Francisco, CA (3 days/week in office)

A senior engineer to take Meanwhile's public API and MCP server from early prototype to the contract outside partners, and their agents, build against.

We are opening the Meanwhile platform up. Brokers, distribution partners, administrators, and auditors all need to integrate with us directly, and increasingly they want to do it through agents rather than through a browser. We're building two things to support that: a public API, and an MCP server that exposes the platform's capabilities to AI agents safely.

The work starts from an early internal prototype, built to serve one of our own integrations, and your job is to take it to a real external product. This is a first-version problem, which is the interesting part and the hard part. The contracts you design will be depended on by outside parties who cannot be asked to redeploy on your schedule, in a regulated business where the data crossing the boundary is policyholder and financial data. Getting the resource model, the auth model, and the versioning story right at the start is worth more than any amount of cleanup later.

You'll own the public surface end to end: design, implementation, security, performance, documentation, and the developer experience of the people building against it. We're looking for someone who wants to go deep here as an individual contributor - the person who owns how the outside world talks to Meanwhile.

What You'll Do

• Design and build Meanwhile's public API - resource modeling, versioning and deprecation policy, idempotency, pagination, error taxonomy, webhooks and event delivery
• Build our MCP server, exposing platform capabilities as tools agents can use safely: least-privilege scoping, clear tool boundaries, and human-in-the-loop on state-changing operations
• Own the authentication and authorization model for external access - OAuth 2.0 / OIDC, scoped credentials, tenant and partner isolation, key lifecycle and rotation
• Build the controls that keep a public surface safe and predictable: rate limiting and quotas, abuse detection, input validation, request signing, comprehensive audit logging
• Design for scale and degrade gracefully - latency budgets, caching, backpressure, load shedding, SLOs, and the observability to know when any of it is slipping
• Write the documentation, reference, and integration guides third parties actually build from, and keep them accurate as the API evolves
• Build the surrounding developer experience: sandbox environment, example integrations, changelog, and a support path for partners who are stuck
• Partner with the engineering teams behind the API to shape internal services into a coherent external contract rather than leaking our internals
• Write production code in Python against PostgreSQL, with client SDKs in other languages a possibility as external adoption grows
• Use AI tooling to move faster, with the judgment to know when its output needs a second look
• Participate in business-hours on-call rotation shared across the engineering team (no nights/weekends)

How We Work

We don't have product managers. You'll work directly with the partners and internal teams who depend on the API to understand what they need, shape the contract, and explain the tradeoffs - that discovery is part of the job, not something that happens before it reaches you.

We lean into AI tooling and you'll have it. It's a real accelerant here, and we expect you to use it well. But a public API is the one surface where mistakes are permanent: once a partner has built against a contract, you live with it. The work still rests on thinking carefully about the interface, the security model, and the failure modes.

Qualifications

Required

• 10+ years of professional software engineering experience
• Substantial experience designing and operating public or partner-facing APIs - not just internal services, but interfaces consumed by engineers outside your company
• Depth in API security: authentication and authorization models, OAuth 2.0 / OIDC, credential and key management, tenant isolation, common attack classes against public endpoints
• Experience scaling an API surface in production - rate limiting, caching, latency and throughput work, graceful degradation, incident response on a surface you can't take down
• Demonstrated ability to produce documentation third parties can integrate from without hand-holding, and a genuine interest in developer experience as a first-class product concern
• Strong Python and relational database experience (PostgreSQL or equivalent)
• Experience supporting external integrators - triaging their problems, and feeding what you learn back into the design
• Fluency with AI development tools, and the judgment to evaluate what they produce
• Comfort with ambiguity and a habit of teaching yourself the domain
• Low-ego approach and a high bar for precision
• Based in the SF Bay Area with the ability to work in-office 3 days per week

What Makes You Stand Out

• Experience building an MCP server, or otherwise designing tool interfaces for AI agents
• Experience launching a v1 public API at a company that hadn't had one before, including the versioning and deprecation policy that came with it
• Fintech, insurance, or other regulated-industry experience, particularly where partner data sharing had contractual or regulatory constraints
• Event-driven and webhook delivery experience - at-least-once semantics, retries, replay, consumer-side idempotency
• SDK authoring, OpenAPI tooling, or API gateway design
• Interest in or experience with cryptocurrency/blockchain technologies
• Startup experience on small engineering teams (<10 people)

Technical Environment

• Backend: Python
• Database: PostgreSQL
• CI/CD: GitHub Actions
• Cloud: AWS

Why Join Us?

• Define the contract: Set the public interface for a platform that doesn't have one yet, without inheriting a decade of someone else's decisions
• Real Ownership: You'll own the entire external surface - API, MCP server, docs, and developer experience
• Unique Domain: Build the integration layer for first-of-their-kind Bitcoin-denominated financial products
• Direct Influence: Small team, flat organization, direct access to leadership
• Ahead of the curve: Agent-facing interfaces are being figured out right now, and you'd be doing that work rather than reading about it
• Benefits:
• Fully covered health, dental, and vision for you and your family
• Meals provided in office
• Two annual company off sites (fully paid)

Our Values

• Keep your word. Honor commitments to clients and each other.
• Build for the future. We measure success in decades; look ahead without losing sight of what matters today.
• Be curious. Our advantage is understanding the world, the market, and each other.
• Have fun. Enjoy the work. Find humor where you can. Rest when needed. Say when you need help.

How to Apply

Email [email removed] with your resume and the role you'd be interested in.