APIs Built for
Production
Not a prototype you'll rewrite in six months. We build custom APIs with authentication, rate limiting, versioning, and full documentation—ready to handle real traffic on day one.
Engineering quality
What separates a good API from a great one
Most API projects deliver working endpoints. We deliver the full surface area: consistent error responses, proper pagination, filtering, caching headers, and a contract your consumers can rely on.
REST or GraphQL
We help you choose the right paradigm. REST for predictable, cache-friendly endpoints. GraphQL when clients need flexible, nested queries. Both built to spec, not to convention.
Authentication done right
JWT with proper expiry and refresh flows, OAuth2 with PKCE for third-party auth, or API key management with scoped permissions. No bolted-on auth that becomes a liability.
Built to survive load
Elixir/Phoenix handles thousands of concurrent connections on modest hardware. Rate limiting, connection pooling, and query optimization are first-class concerns—not afterthoughts.
Deliverables
Everything shipped with the project
Your frontend team, mobile developers, and third-party partners get a complete, documented API—not a URL and a promise.
- OpenAPI / Swagger documentation.
- Interactive docs with every endpoint, parameter, response schema, and error code. Your integrators can explore and test without asking you questions.
- Rate limiting and throttling.
- Per-consumer rate limits with proper 429 responses and Retry-After headers. Protect your infrastructure and enforce fair use without blocking legitimate traffic.
- Pagination, filtering, and sorting.
- Cursor-based or offset pagination with consistent envelope responses. Field filtering, multi-column sorting, and full-text search built into list endpoints from the start.
- API versioning strategy.
- Version your API from day one so you can evolve without breaking existing clients. URL versioning, header-based versioning, or deprecation notices—designed around your release cadence.
- Comprehensive error handling.
- Consistent error envelope with machine-readable codes, human-readable messages, and field-level validation errors. No more "something went wrong" for your consumers to debug.
- Monitoring and observability.
- Request logging, latency metrics, error rate alerting, and health check endpoints. You'll know about a problem before your customers do.
- PostgreSQL schema and migrations.
- Database design that reflects your domain, not just your UI. Proper indexes, foreign key constraints, and migration files your team can run with confidence.
- Third-party integrations and webhooks.
- Stripe, Twilio, SendGrid, or any service your business depends on. Outbound webhooks with retry logic and signature verification so your integrations are reliable under failure.
Why Cobalt Sentry
Experience meets modern delivery
- 20+ Years Shipping Software
- Elixir, Phoenix, Swift, and Astro in production. Not a generalist shop that Googles your stack after the contract is signed.
- Fixed-Price, No Surprises
- You know the cost before we write a line of code. No hourly billing, no scope creep invoices, no "we need another sprint."
- You Own Everything
- Full source code, deployment credentials, and documentation on handoff. No lock-in, no retainer required to keep the lights on.
Build vs. buy
When custom makes sense
Off-the-shelf API platforms are excellent until your business logic doesn't fit their model. Here's when we recommend building custom.
Your data model is unique
Generic BaaS platforms force your domain into their schema. When your business logic is the product, a custom API lets your data model serve the business—not the other way around.
You need predictable performance
Shared infrastructure means unpredictable latency. Elixir/Phoenix runs on the Erlang VM—the same foundation that powers systems with millions of concurrent connections and 99.999% uptime.
You're building a mobile backend
Mobile apps need APIs that are fast on poor connections, handle offline-then-sync patterns, and push real-time updates efficiently. That requires a backend designed for it from the start.
Integration complexity is your moat
When your value is in orchestrating multiple third-party services—payments, messaging, logistics, identity—a custom integration layer gives you control over reliability, error handling, and retry logic.
Process
From requirements to production
A structured process that gets working code in front of you fast, then hardens it for the real world.
- 1
Spec and data modeling
We review your requirements and propose an endpoint structure, authentication strategy, and data model before writing a line of code. No surprises mid-build.
- 2
Core endpoints first
Auth and your most critical endpoints ship first. Your team can begin integration work while we continue building—no waiting on the full spec to start.
- 3
Harden and expand
Remaining endpoints, integrations, edge cases, and error scenarios. Rate limiting, caching, and performance tuning happen here—not as a last-minute patch.
- 4
Deploy with full docs
Production deployment with SSL, monitoring, and health checks. OpenAPI docs, example requests, and a handoff session so your team can own it immediately.
Fixed-Price API Development
Fixed-price projects, no hourly billing. Scope is agreed upfront so you know exactly what you're getting and what it costs.
Ready to build your API?
Share your requirements and we'll respond with a project proposal—endpoint scope, architecture approach, timeline, and fixed price—within 24 hours.
Start Your API Project
Tell us about your API: what it needs to do, who will consume it, and any existing systems it needs to connect to.