Custom API development that other software can rely on
Gjethe designs and builds custom APIs (REST, GraphQL and WebSocket) for mobile and web apps, partner integrations and public developer platforms. Every API comes with authentication, rate limiting, consistent error handling, versioning, automated tests and OpenAPI documentation, and is deployed with monitoring on your own cloud.
- Free first consultation
- Written quote for your project
- Flexible payment milestones
At a glance
- Styles
- REST, GraphQL, WebSocket, webhooks
- Docs
- OpenAPI with interactive reference
- Security
- OAuth 2.0, API keys, rate limits
- Stack
- Node.js or Python
Definition
What is custom API development?
An API (application programming interface) is a defined way for software systems to talk to each other. A custom API exposes your data and business logic to your own apps, partners or customers in a controlled, documented way.
An API is a promise: once other software depends on it, changing it carelessly breaks things you don't control. That's why API work is as much about design and documentation as code, clear resource names, predictable errors, versioning and limits. We design the contract first, agree it with the people who'll use it, then build and test against it.
Who is it for?
Teams building mobile or web apps
Your app needs a secure, fast backend that serves exactly the data each screen needs.
SaaS companies opening up
Customers and partners want to integrate with your product through a public API and webhooks.
Businesses with valuable data
You want to expose catalogue, availability or pricing data to partners in a controlled way.
Companies with legacy systems
An older system needs a modern API in front of it so new apps can use its data safely.
What's included, and what you keep
What's included
- API design workshop and resource modelling
- OpenAPI or GraphQL schema agreed before build
- Authentication with OAuth 2.0, JWT or API keys
- Role-based authorisation per endpoint
- Input validation and consistent error format
- Pagination, filtering and sorting
- Rate limiting and abuse protection
- Versioning strategy
- Webhooks with signing and retries
- Automated contract and integration tests
- Interactive documentation
- Deployment with logging and monitoring
What you receive
Handed over at the end. Yours to keep.
- Deployed API on your cloud account
- Source code and test suite
- OpenAPI or GraphQL schema
- Interactive API documentation
- Postman or Bruno collection for testing
- Runbook for operations and on-call
REST, GraphQL or WebSocket?
| Style | Best for | Trade-off |
|---|---|---|
| REST | Most APIs; simple to cache, document and consume | Clients may need several calls for complex screens |
| GraphQL | Many clients needing different shapes of the same data | Harder to cache; needs query limits |
| WebSocket | Live updates: chat, dashboards, collaboration | Persistent connections need extra infrastructure |
| Webhooks | Telling other systems when something happens | Receivers must handle retries and duplicates |
What makes an API pleasant to integrate with?
Predictability. Resources named in plain language, the same pagination and error format everywhere, and timestamps and IDs that behave the same across endpoints. Developers should be able to guess how an endpoint works before reading its documentation.
Good documentation with real examples, a sandbox or test keys, and clear explanations of limits and errors. Most integration support requests come from missing documentation rather than bugs.
And stability. Breaking changes go into a new version with a deprecation period, so existing integrations keep working while partners upgrade on their own schedule.
API security essentials we build in
- Every request authenticated; no anonymous write access
- Authorisation checked per resource, not just per endpoint
- Input validated against the schema
- Rate limits per key and per IP
- Secrets stored in a vault, never in code
- Logging that records access without storing sensitive data
- Dependency and vulnerability scanning in CI
Who uses the APIs we build
Your own apps
Mobile and web front ends that need a fast, secure backend shaped around their screens.
Partners
Resellers, suppliers or marketplaces exchanging orders, stock or pricing with you.
Developers
Customers building on your platform through a public API, SDKs and webhooks.
Internal systems
Services inside your company that need a shared, documented way to exchange data.
How custom API development works, step by step
Every step has a clear output you can review. Timing is agreed in your quote.
- 1
Consumers and use cases
Who will call the API, for what, and how often.
- 2
Contract design
Resources, endpoints and payloads written as an OpenAPI or GraphQL schema and reviewed with consumers.
- 3
Build
Implementation against the contract, with validation, auth and error handling.
- 4
Test
Automated contract, integration and load tests.
- 5
Document
Interactive reference, examples and onboarding guide for developers.
- 6
Deploy and observe
Production deployment with dashboards, alerts and usage analytics.
Tools, and what shapes your quote
Pricing is based on your project and agreed in your quote. These are the things that move it.
| Factor | Why it matters |
|---|---|
| Number of resources and endpoints | Each resource needs design, validation, permissions and tests. |
| Authentication model | Partner OAuth flows and fine-grained permissions take more work than simple API keys. |
| Data sources | Wrapping legacy databases or several internal systems adds integration work. |
| Real-time needs | WebSockets and event streams require additional infrastructure. |
| Performance targets | High request volumes need caching, load testing and scaling plans. |
| Public developer experience | A developer portal, sandbox and SDKs are extra deliverables. |
| Area | Tools |
|---|---|
| Node.js | Fastify, NestJS, Express, tRPC |
| Python | FastAPI, Django REST Framework |
| GraphQL | Apollo Server, GraphQL Yoga, Pothos |
| Data | PostgreSQL, Redis, message queues |
| Docs & testing | OpenAPI, Scalar, Postman, k6 |
Common mistakes to avoid
What we see go wrong most often, and how a good project avoids it.
Building before agreeing the contract
Changing endpoints after apps depend on them is expensive. Agree the schema first.
Inconsistent errors
Each endpoint returning errors differently forces integrators to write special cases everywhere.
No versioning plan
Without one, every improvement risks breaking existing integrations.
Returning everything
Over-fetching exposes data unnecessarily and slows responses. Return what the consumer needs.
Documentation as an afterthought
An undocumented API generates support requests and slows every integration.
Frequently asked questions
REST or GraphQL?
REST is simpler to cache and the right default for most APIs. GraphQL helps when many clients need different shapes of the same data, such as a web app and a mobile app sharing one backend.
Do you document the API?
Yes. Every API ships with an OpenAPI or GraphQL schema and interactive documentation, so your team or your customers can integrate without asking us.
Can you build an API on top of our existing database?
Yes. We can expose existing data through a new API layer, adding authentication, validation and caching without changing the underlying system.
How do you handle breaking changes?
Through versioning: changes that would break consumers go into a new version, and old versions are deprecated with notice.
Can the API send events to other systems?
Yes, through signed webhooks with retries, or through message queues for internal systems.
How do you protect the API from abuse?
With authentication, per-key rate limits, input validation, request size limits and monitoring that alerts on unusual patterns.
Where is the API hosted?
On your own cloud account (AWS, Azure, Google Cloud or Vercel) with logs and monitoring you can access.
Can you build SDKs for our API?
Yes. SDKs for JavaScript or Python can be generated from the schema and refined for a better developer experience.
Do you load-test APIs?
Yes, when traffic expectations call for it, using tools such as k6 to find bottlenecks before launch.
Can you take over an existing API?
Yes. We review the code, document the endpoints, add tests and monitoring, and then improve or extend it.
How do you version an API?
Usually with a version in the URL or a header. Additive changes (new fields, new endpoints) don't need a new version; anything that would break existing clients does, with a deprecation period for the old one.
Can you add an API to a no-code or low-code product?
Often. If your data lives in a tool such as Airtable or a database behind a no-code app, we can build an API layer in front of it with proper authentication and validation.
Related services
API Integration
Connect the tools you already use so data flows on its own.
Web Applications & SaaS
Portals, dashboards and subscription products.
Custom Software Development
Software built around your exact process.
DevOps & CI/CD
Automated pipelines, containers and infrastructure as code.
Cloud Deployment
Vercel, AWS, Azure and Google Cloud set up properly.
Custom API Development by industry
Build your API.
Tell us what you need. You get an honest assessment, a clear plan and a written quote. The first consultation is always free.
- What happens next
- 1You tell us what you need
- 2We aim to reply within 24 hours with questions
- 3You get a written quote for your project