Overview
An API is the contract between systems. Whether you are exposing your platform's functionality to external developers, connecting your own internal services to each other, enabling a mobile or web frontend to communicate with your backend, or providing data feeds to third-party consumers — the quality of that contract determines how reliably everything built on top of it works.
We design and build custom APIs from the ground up. REST APIs for request-response interactions, WebSocket services for real-time bidirectional communication, and hybrid architectures that combine both where the use case demands it. Our APIs are built to be consumed — with clear, consistent interfaces, proper authentication, meaningful error responses, and the performance characteristics the use case requires.
REST API Development
REST remains the dominant paradigm for API design because it maps naturally to the way the web works, is supported by every HTTP client in existence, and produces interfaces that are straightforward to understand, document, and consume.
Building a REST API that works well in production goes substantially beyond defining a few endpoints and returning JSON. The decisions made at the design stage — resource modelling, versioning strategy, authentication approach, error response structure, pagination conventions — propagate through every client built on top of the API and become increasingly expensive to change later. We get these decisions right upfront.
Resource design and URL structure. We model APIs around resources and relationships that reflect the domain accurately, with URL structures that are predictable and navigable. Endpoints are named for what they represent, not for the operations performed on them. HTTP methods are used semantically — GET for retrieval, POST for creation, PUT and PATCH for updates, DELETE for removal — so that clients can rely on standard HTTP semantics without consulting documentation for every interaction.
Versioning. APIs change. Clients that depend on them cannot always change at the same time. We design versioning strategies upfront — URL path versioning, header-based versioning, or content negotiation depending on the deployment context — so that breaking changes can be introduced in new versions without disrupting existing consumers.
Authentication and authorisation. We implement authentication appropriate to the use case — API key authentication for server-to-server integrations, OAuth2 with PKCE for user-delegated access, JWT bearer tokens for stateless authentication, and HMAC request signing for high-security contexts where request integrity verification is required. Authorisation is implemented at the resource level, not just the endpoint level, ensuring that authenticated clients can only access and modify the resources they are permitted to.
Request validation. Every request is validated before processing. Required fields, type constraints, value ranges, format validation, and cross-field dependencies are all enforced at the API boundary, with validation errors returned as structured, actionable responses that tell the client exactly what is wrong and how to fix it.
Error handling. The quality of an API's error responses is one of the most reliable indicators of its overall quality. We return structured error responses with consistent format, appropriate HTTP status codes, machine-readable error codes for programmatic handling, and human-readable messages for debugging — across every endpoint, consistently.
Pagination, filtering, and sorting. Any endpoint that returns collections needs well-designed pagination. We implement cursor-based pagination for large or frequently updated datasets where offset pagination produces inconsistent results, and offset pagination where simplicity is more important than perfect consistency. Filtering and sorting parameters are documented and validated, with sensible defaults that prevent accidental full-table scans.
Rate limiting and throttling. APIs exposed to external consumers need rate limiting to prevent abuse and ensure fair resource distribution. We implement rate limiting with appropriate granularity — per API key, per user, per endpoint — with rate limit headers in responses so clients can manage their request pacing proactively.
WebSocket API Development
WebSocket connections are the right architecture when the communication pattern is not request-response but continuous, bidirectional, or event-driven. Real-time dashboards, live trading feeds, collaborative applications, chat systems, live notifications, and streaming data services all benefit from WebSocket architecture over repeated REST polling.
Building a production WebSocket service requires solving a set of engineering problems that REST APIs do not face:
Connection management at scale. A WebSocket server maintains a persistent connection with every connected client simultaneously. Managing thousands of concurrent connections efficiently — with low memory overhead per connection, proper cleanup when connections close, and graceful handling of client reconnections — requires deliberate architecture from the start.
Message protocol design. Unlike REST where the protocol is largely defined by HTTP, WebSocket services require explicit message protocol design. We define typed message schemas, message routing conventions, acknowledgement patterns where reliable delivery matters, and error message structures — producing a protocol that is as clear and predictable as a well-designed REST API.
Rooms, channels, and subscription management. Most real-world WebSocket applications need to route messages selectively — to specific users, to subscribers of specific data streams, to participants in specific sessions. We implement subscription management systems that allow clients to subscribe to the data streams they need without receiving everything the server produces.
Presence and state synchronisation. Applications where users need to see each other's current state — collaborative tools, multiplayer systems, live trading interfaces — require presence tracking and state synchronisation built into the WebSocket layer. We design these systems with eventual consistency where appropriate and strong consistency where the application requires it.
Horizontal scaling. A single WebSocket server has connection limits. Scaling horizontally — across multiple server instances — requires a shared state layer so that messages can be routed to connections on any instance. We design WebSocket services with Redis pub/sub or equivalent message bus architectures that enable horizontal scaling without breaking the connection routing logic.
Fallback and degradation. Not every network environment supports persistent WebSocket connections reliably. We design WebSocket services with fallback strategies — Server-Sent Events or long polling — for clients that cannot maintain WebSocket connections, ensuring the application remains functional across different network conditions.
Hybrid Architectures
Many real-world applications benefit from combining REST and WebSocket in a single API surface — REST for operations that are naturally request-response (authentication, resource creation, configuration, bulk operations) and WebSocket for the real-time data streams and event notifications that polling cannot serve efficiently.
We design hybrid architectures that present a coherent interface to API consumers, with clear conventions for when to use which transport and shared authentication across both.
API Security
Security is not a layer added to an API after it is built — it is a set of decisions made throughout the design and implementation process. Every API we build is designed with security as a first-class concern:
Transport security. All APIs are served over TLS. Certificate management, cipher suite configuration, and HSTS headers are handled correctly, not left at framework defaults.
Input sanitisation. Every input is treated as potentially hostile. SQL injection, command injection, path traversal, and XML external entity attacks are defended against at the input handling layer, not relied upon downstream systems to handle.
Sensitive data handling. Credentials, tokens, personally identifiable information, and financial data are handled with appropriate care — never logged in plain text, encrypted at rest where stored, and excluded from error responses and debug output.
Audit logging. Every authenticated request is logged with the identity of the caller, the resource accessed, the operation performed, and the outcome. This audit trail is essential for security incident investigation, compliance requirements, and operational debugging.
CORS configuration. Cross-origin resource sharing is configured explicitly and correctly — not set to wildcard allow-all as a debugging convenience that never gets tightened in production.
API Documentation
An API without documentation is not finished. We deliver every API with comprehensive documentation that enables consumers to integrate without requiring support:
OpenAPI / Swagger specification. Every REST API is documented with a complete OpenAPI specification that describes every endpoint, every request parameter, every response schema, and every error code. This specification serves as both human-readable documentation and machine-readable contract that can be used to generate client SDKs, validate requests, and power interactive documentation interfaces.
WebSocket protocol documentation. WebSocket message protocols are documented with the same rigour — message types, schemas, sequencing requirements, subscription conventions, and error handling expectations all documented explicitly.
Integration guides. Beyond reference documentation, we produce integration guides for the most common use cases — authentication flows, pagination patterns, error handling best practices, and rate limit management — that give integrating developers a fast path to working implementations.
Performance and Scalability
API performance directly affects the user experience of every application built on top of it. We design APIs with performance characteristics appropriate to their use case:
Response time targets. Performance requirements are defined upfront and validated during development. Database query optimisation, caching strategy, and connection pooling are all considered as part of the API design, not retrofitted after performance problems appear in production.
Caching. We implement caching at appropriate layers — HTTP caching headers for client and proxy caching of appropriate responses, application-level caching for expensive computations and frequently accessed data, and cache invalidation strategies that keep cached data consistent with source data.
Asynchronous processing. Operations that are too expensive to complete within a synchronous request cycle — report generation, bulk data processing, external API calls with unpredictable latency — are handled asynchronously with job queuing and status polling or webhook notification patterns.
Database design. API performance is frequently limited by database performance. We design database schemas with the API's query patterns in mind, with appropriate indexing, query optimisation, and connection pool sizing.
Technologies We Build APIs With
- Rust / Axum — highest performance APIs, latency-critical services, high-concurrency WebSocket servers
- C# / ASP.NET Core — enterprise APIs, Microsoft ecosystem integration, complex business logic
- PHP / Laravel — rapid API development, CMS-adjacent backends, straightforward CRUD services
- Next.js API Routes — frontend-adjacent APIs, BFF patterns, serverless-compatible deployments
- SQL (PostgreSQL, MySQL, SQLite) — relational data storage for all API backends
- Redis — caching, session storage, WebSocket pub/sub for horizontal scaling
- Auth0 / JWT / OAuth2 — authentication and authorisation across all API types
- OpenAPI / Swagger — API specification and documentation for all REST APIs
- Docker — containerised API deployment for consistent environments across development and production
Who Needs a Custom API
You need a custom API when off-the-shelf solutions do not fit your data model, your performance requirements, your security constraints, or your integration needs. Common scenarios include:
A platform that needs to expose its functionality to third-party developers or partners. A mobile or web application that needs a backend tailored to its specific data requirements. An internal system that needs to share data with other internal systems without tight coupling. A data product that needs to deliver feeds to multiple consumers with different access levels and rate limits. A real-time application — trading platform, collaborative tool, live dashboard — that needs WebSocket infrastructure designed for its specific communication patterns.
If you are building on top of an existing API that does not quite fit and spending significant engineering effort working around its limitations, a custom API built to your exact requirements is frequently the right answer.
Let's Design Your API
Good API design is one of the highest-leverage investments a software project can make. The interface you define today will be implemented by clients, consumed by applications, and depended upon by systems for years. We bring the experience to get it right the first time.