APIs designed to
last longer than
the team that built them
An API is a contract. Break it carelessly and you break every product built on top of it. We design RESTful and GraphQL APIs with versioning, documentation, and error handling baked into the architecture from the first endpoint - not retrofitted before launch.
Every type of API. One engineering standard.
Whether you need a straightforward REST API, a flexible GraphQL layer, or a distributed microservices mesh - we design for the consumers of the API, not just the team building it.
RESTful API Design & Development
REST APIs built around resource-oriented design, consistent error responses, clear versioning strategy, and hypermedia links where they add genuine value. We write the OpenAPI specification first and generate server stubs from it - ensuring the documentation never drifts from the implementation.
GraphQL API Development
Schema-first GraphQL APIs with DataLoader for N+1 prevention, field-level authorisation, query depth limiting, and persisted queries for production performance. We design the schema around client needs - not the backend data model.
Microservices Architecture
Service decomposition, API gateway design, inter-service communication patterns, and event-driven architecture with message queues. We define service boundaries around business domains - not technical convenience - to avoid the distributed monolith trap.
Third-Party API Integrations
Clean, resilient integrations with payment gateways, CRMs, ERPs, marketing platforms, and data providers - wrapped in abstraction layers so a vendor change doesn't ripple through your entire codebase.
API Security & Authentication
OAuth 2.0 and OpenID Connect implementation, JWT handling, API key management, scopes, and RBAC. Rate limiting, IP allowlisting, request signing, and OWASP API Security Top 10 coverage built in from the start.
Spec first, code second —
always
API Design & Contract
Define resource models, URL structure, request/response schemas, error codes, and versioning strategy in an OpenAPI spec - reviewed and agreed before any development begins.
Authentication & Security Layer
Implement OAuth 2.0, JWT validation, rate limiting, CORS policy, and request signing. Security is designed into the API architecture, not layered on afterwards.
Core Endpoint Development
Build endpoints against the agreed spec with full test coverage. Integration tests, contract tests, and load tests run in CI on every commit. No endpoint ships without passing all three.
Docs, SDK & Deployment
Auto-generated developer documentation from the OpenAPI spec, optional SDK generation for key languages, staging and production deployment, monitoring setup, and developer onboarding guide.
REST, GraphQL, or gRPC - the decision matters more than most teams realise
Each protocol solves a different problem. We make the recommendation based on your consumers, your team's operational capabilities, and your performance requirements - not on what's fashionable this quarter.
REST - The sensible default for most APIs
REST remains the right choice for the majority of public-facing and partner APIs. The conventions are widely understood, tooling is mature, caching is straightforward, and any client in any language can consume it without specialised libraries. We follow Fielding's constraints properly - not just "it uses HTTP and returns JSON."
GET /v2/orders/ord_8xwvl
Authorization: Bearer {token}
// Response 200 OK
{
"id": "ord_8xwvl",
"status": "fulfilled",
"total": 148.50,
"currency": "GBP",
"_links": {
"self": "/v2/orders/ord_8xwvl",
"user": "/v2/users/usr_4k9mxp2q"
}
}
Uniform resource-based URLs
Predictable, self-documenting endpoint structure that any developer can navigate without reading the full spec.
HTTP semantics used correctly
GET is idempotent, POST creates, PUT replaces, PATCH updates, DELETE removes. Status codes mean what they're supposed to mean.
OpenAPI spec always in sync
We write the spec first and generate server stubs from it - the documentation is never a post-hoc retrofit.
Caching at every layer
ETag support, Cache-Control headers, and CDN-compatible endpoint design included as standard.
GraphQL - Right when clients need flexibility
GraphQL earns its complexity when you have multiple client types with genuinely different data needs - a mobile app, a web dashboard, and a third-party integration all hitting the same API but wanting different shapes of data. It eliminates over-fetching and under-fetching, but introduces query complexity and N+1 challenges that require careful schema design and DataLoader implementation to handle correctly.
query GetUserOrders($userId: ID!, $first: Int!) {
user(id: $userId) {
name
email
orders(first: $first, status: FULFILLED) {
edges {
node {
id
total
createdAt
items { sku quantity }
}
}
pageInfo { hasNextPage endCursor }
}
}
}
Schema-first design
The schema is the contract. We define it before writing resolvers, and document every field, type, and directive.
N+1 prevention with DataLoader
Batch-loading for all related entity fetches. No GraphQL endpoint ships without DataLoader where association queries exist.
Query complexity analysis
Depth limits, complexity scoring, and introspection controls protect the API from expensive query abuse.
Real-time with subscriptions
WebSocket-based subscriptions for live data use cases - order status, notifications, collaborative editing.
gRPC - When latency and throughput are the priority
gRPC is the right choice for internal microservice communication where you need high throughput, bidirectional streaming, and strong typing across service boundaries. Protocol Buffers give you a typed contract between services that fails at compile time rather than at runtime, and binary serialisation is significantly faster than JSON for high-volume internal traffic.
syntax = "proto3";
service OrderService {
rpc GetOrder (OrderRequest) returns (Order);
rpc StreamOrders (UserRequest) returns (stream Order);
rpc BatchCreateOrders (stream CreateOrderRequest)
returns (BatchResult);
}
message Order {
string id = 1;
string status = 2;
double total = 3;
int64 created_at = 4;
}
Protobuf schema validation
Strongly-typed contracts between services that catch breaking changes at compile time, not in production.
Bidirectional streaming
Client, server, and bidirectional streaming for high-volume data pipelines and real-time communication between services.
Significantly lower latency
Binary serialisation and HTTP/2 multiplexing reduce internal service call overhead compared to REST/JSON at scale.
Code generation
Client and server stubs generated from the proto definition across Go, Node.js, Python, and Java simultaneously.
WebSockets - For genuinely real-time requirements
WebSockets are appropriate when data changes that the client needs to see happen faster than polling can realistically handle - sub-second updates, collaborative features, or push notifications that need to be instant. We implement connection management, heartbeat handling, reconnection logic, and horizontal scaling with Redis pub/sub so the real-time layer stays reliable under load.
// Server (Node.js)
const wss = new WebSocketServer({ port: 8080 });
wss.on('connection', (ws, req) => {
const userId = authenticate(req);
subscribeToUserEvents(userId, (event) => {
ws.send(JSON.stringify({
type: event.type,
payload: event.data,
ts: Date.now()
}));
});
ws.on('message', handleClientMessage);
ws.on('close', () => unsubscribe(userId));
});
Connection lifecycle management
Heartbeat pings, graceful reconnection with exponential backoff, and connection state tracking included as standard.
Horizontal scaling with Redis
Pub/sub message broadcasting ensures real-time events reach clients regardless of which server instance holds their connection.
Room and channel architecture
Scoped subscriptions so clients only receive events relevant to them - no unnecessary data transmission.
Fallback to SSE or polling
Server-Sent Events or long-polling fallback for environments where WebSocket connections are blocked by firewalls or proxies.
Webhooks - The right way to push events to consumers
Webhooks are often the simplest and most reliable way to notify external systems about events in your platform. Done well, they include retry logic with exponential backoff, event ordering guarantees, payload signing so consumers can verify authenticity, and a delivery log so consumers can replay missed events. Done badly, they're a support ticket waiting to happen.
// Webhook dispatcher
async function dispatchWebhook(endpoint, event) {
const payload = JSON.stringify(event);
const signature = createHMAC(
process.env.WEBHOOK_SECRET,
payload
);
const res = await fetch(endpoint.url, {
method: 'POST',
headers: {
'Content-Type': 'application/json',
'X-Sequere-Signature': signature,
'X-Sequere-Timestamp': Date.now()
},
body: payload
});
return res.status;
}
HMAC payload signing
Every webhook payload is signed with a consumer-specific secret. Consumers can verify authenticity before processing.
Retry with exponential backoff
Failed deliveries retry up to 72 hours with exponential backoff - consumers don't miss events because of temporary downtime.
Delivery log and replay
Complete delivery history with one-click replay for any failed event. Consumers can self-serve missed events without contacting support.
Endpoint health monitoring
Automatic detection and alerting when consumer endpoints start returning errors, before the consumer notices.
What makes an API genuinely good - and how we make sure every one we ship qualifies
A good API is invisible to the developers consuming it. Everything is where they'd expect it to be, errors tell them what actually went wrong, and the documentation matches what the API actually does.
Talk to an API engineerSpec-first - documentation that never lies
We write the OpenAPI specification before writing any implementation code. Server stubs are generated from the spec, which means the documentation and the actual API behaviour are structurally identical by construction - not by discipline. When the spec changes, the tests catch any implementation drift automatically.
Versioning strategy from the first endpoint
Breaking changes are inevitable. The question is whether you handle them gracefully or with a hard cutover that breaks integrators. We design versioning strategy before the first endpoint is built - URI versioning, header versioning, or sunset policies - so future changes can be made without forcing immediate migration.
Errors that actually help developers debug
The standard for API error responses is embarrassingly low. Most return a HTTP status code and a generic message. We return structured error objects with a machine-readable code, a human-readable message, a link to the relevant documentation section, and field-level validation details where relevant. Developers fix problems faster. Support tickets go down.
Performance engineered in, not optimised later
Pagination on every collection endpoint. N+1 query prevention via DataLoader or eager loading strategy. Database indexes reviewed for every query path. Response compression enabled. Connection pooling configured. We treat these as requirements with acceptance criteria - not suggestions applied when someone complains the API is slow.
Developer experience is a first-class concern
An API nobody can figure out how to use is a liability, not an asset. We provide auto-generated interactive documentation (Scalar or Redoc), Postman collections, code samples in at least three languages, and - for partner APIs - SDK generation from the OpenAPI spec. Developer time to first successful request is a metric we track.
Framework-agnostic.
Production-opinionated.
We select based on your team's operational capabilities, performance requirements, and what you'll actually be able to maintain at 2am when something breaks.
APIs we've shipped - and what they handle today
Production results from APIs handling real transaction volumes across fintech, healthtech, and enterprise platforms.
Payment & Ledger API
Core REST API powering a fintech platform - handling payment initiation, transaction ledger, FX conversions, and compliance reporting across 14 currencies. PCI-DSS compliant, SOC 2 Type II audited.
FHIR-Compliant Patient Data API
HL7 FHIR R4 REST API enabling secure exchange of patient records between hospital systems, GP practices, and insurers. Full audit trail, role-scoped access, and end-to-end encryption at rest and in transit.
Multi-Vendor Marketplace API
GraphQL API serving a multi-vendor marketplace - products, inventory, orders, and vendor payouts all in a single schema. Real-time inventory updates via subscriptions, and automated payout calculations across 2,000+ sellers.
Questions we get before every API project
Straight answers on versioning, documentation, costs, and timeline. Anything else - ask directly.
Let's design your API before we write a single line of code
Book a free 45-minute call with one of our API engineers. We'll map out your endpoints, talk through authentication requirements, and give you a clear scope - timeline and cost - before any commitment.