API Development

API Development for Complex SaaS Data Models

SaaS products with rich, interconnected data models expose a fundamental tension in API design: your internal data structure is optimised for your application, but your API consumers need a surface that is intuitive, performant, and stable across versions. When your product manages hundreds of entity types with deep relationships — think project management tools, analytics platforms, or CRM systems — getting the API design wrong means either crippling the developer experience or creating a maintenance burden that grows with every new feature. We design and build GraphQL and REST APIs specifically for SaaS products where the data model is the product.

Schema-First Design Process

We treat the API schema as a contract that drives both implementation and client code generation. This approach eliminates drift between documentation and reality.

1. Domain Modelling: We map your entire domain — entities, relationships, access patterns, and query shapes — into a formal schema before writing any resolver or controller code. For GraphQL, this is a complete SDL schema. For REST, this is an OpenAPI 3.1 specification with JSON Schema definitions for every request and response body.
2. Pagination Strategy: We implement cursor-based pagination for GraphQL connections and keyset pagination for REST endpoints. Unlike offset-based pagination, these approaches perform consistently regardless of dataset size — a critical requirement for SaaS products where tenant data grows unboundedly.
3. Authorisation Layer: We build field-level authorisation that controls not just which records a user can access, but which fields within those records are visible based on their role, plan tier, and tenant context. Sensitive fields are masked or omitted rather than returning 403 errors, which creates a cleaner developer experience.
4. Code Generation Pipeline: From the schema, we generate TypeScript client SDKs, API documentation, request validators, and mock servers. Changes to the schema automatically propagate to all generated artifacts, keeping your entire API ecosystem in sync.

Deliverables

Every API engagement produces a production system with the tooling and documentation that turns your API into a genuine developer platform.

• GraphQL API with schema-first SDL, DataLoader batching, and persisted query support — or REST API with OpenAPI 3.1 spec and JSON Schema validation
• Cursor-based pagination with configurable page sizes and total count estimation for large collections
• Field-level authorisation middleware with role, plan-tier, and tenant-scoped permission rules
• Tiered rate limiting with per-key quotas, burst allowances, and usage tracking endpoints
• Webhook delivery system with at-least-once guarantees, exponential backoff retries, and a delivery log dashboard
• Generated TypeScript SDK published to npm for your API consumers

When Schema-First API Design Matters

Your product has a data model with dozens of entity types and complex relationships that need to be exposed through a public API. Your current API has grown endpoint-by-endpoint without a coherent design, and third-party developers are struggling to build integrations. You are launching a marketplace or partner ecosystem and your API quality will directly determine partner adoption. Or your mobile and web clients are making too many requests because the API was not designed to serve their specific query shapes efficiently.

Why SaaS Development London for API Architecture

We have designed GraphQL schemas serving millions of queries daily and REST APIs consumed by thousands of third-party applications. Our engineers understand the performance implications of N+1 query patterns in GraphQL resolvers, the security considerations of exposing filtered data through introspection, and the versioning strategies that allow you to evolve a public API without breaking existing consumers. That depth of experience means your API is designed for the integrators you will have in two years, not just the ones you have today.

If your SaaS product needs an API that matches the complexity of your data model, book a free API architecture consultation to discuss your specific requirements.