Development
API and backend development
The backend is the invisible part of an application: it stores data, enforces business rules, manages authentication and exposes APIs (application programming interfaces) consumed by your web and mobile apps and your partners. A well-designed API lets several interfaces and systems share the same logic without duplicating it.
Agencei builds REST and GraphQL APIs and backend services for software vendors, companies opening their data to partners, product teams that need a backend for their mobile app, or information systems where several components must communicate.
We work with Node.js, Spring Boot and Python depending on your ecosystem, delivering versioned, documented, tested and monitored APIs, ready to be consumed by your teams and your customers.
When do we step in?
Providing a backend for a mobile or web app
Your interface needs an API for authentication, data, notifications and payments. We design the backend together with the API contract the interface expects.
Opening your data to partners
Distributors, customers or platforms want to integrate with your system. A documented public API, with access keys, quotas and logging, replaces file exports.
Connecting several systems
ERP, CRM, invoicing tool and e-commerce site exchange data through fragile scripts. An API layer and asynchronous processing make these exchanges reliable.
Replacing a backend that no longer handles the load
Growing response times, outages at peak hours, inefficient database queries: we audit and rebuild critical services.
Breaking up a monolith
A single application that has become too large to deploy with confidence. We progressively extract autonomous services, without a full rewrite.
How we work
- 1
API contract design
We define resources, operations, formats and error codes with the API consumers, and formalize everything as an OpenAPI specification or GraphQL schema before coding.
- 2
Data modelling and architecture
Database choice, relational or document model, service breakdown, caching and asynchronous processing strategy.
- 3
Development and testing
Implementation with unit and integration tests, input validation, error handling, consistent pagination and filtering.
- 4
Security and access management
Authentication (OAuth 2.0, JWT, API keys), role- or resource-based authorization, rate limiting, protection against common attacks.
- 5
Documentation and test environment
Documentation generated from the specification, call examples, sandbox environment for your partners and your teams.
- 6
Deployment and monitoring
Containerization, automated deployment, structured logs, metrics and alerts on response times and errors.
Technologies we use
- Node.js
- NestJS
- TypeScript
- Spring Boot
- Python (FastAPI)
- REST
- GraphQL
- OpenAPI
- PostgreSQL
- Redis
- RabbitMQ or Kafka
- Docker
Related expertise
Why choose Agencei?
The API contract before the code
We specify the API with those who will consume it, which avoids back-and-forth between front-end, mobile and backend teams and allows parallel development.
Three ecosystems mastered
Node.js, Spring Boot and Python: we choose based on your team and your existing systems, not on an internal preference.
Performance measured, not assumed
Load testing, query analysis and caching strategy are part of the delivery, not a later project.
APIs that others can consume without us
Up-to-date documentation, clear versioning, test environment: your partners and future teams integrate without depending on us.
In brief
- What is this service?
- Design and development service for REST and GraphQL APIs and backend services with Node.js, Spring Boot or Python, including security, documentation, testing and monitoring.
- Who is it for?
- Software vendors, product teams that need a backend for their app, companies opening their data to partners or needing to connect several systems.
- What problem does it solve?
- Having a reliable, secure and documented server layer that your interfaces and partners can consume without duplicating business logic.
- How long does it usually take?
- From a few weeks for the backend of a focused application to several months for an API platform open to partners.
- What factors influence the price?
- Number of resources and operations, complexity of business rules, security and compliance requirements, expected volumes and load, integrations with existing systems.
- How does the engagement run?
- API contract design with consumers, data modelling and architecture, development with tests, security hardening, documentation and sandbox, deployment and monitoring.
- What are the risks?
- Unstable API contract that breaks consumers, insufficient security on exposed data, performance not tested under load, missing documentation creating vendor dependence.
- What alternatives exist?
- A backend as a service (Firebase, Supabase) for a prototype, an integration platform (iPaaS) for simple exchanges between market tools, or extending an existing backend.
Frequently asked questions
REST or GraphQL: which should we choose?
REST remains the default choice for a public or partner-facing API, as it is simple to document, cache and consume. GraphQL is worthwhile when several interfaces have very different data needs and want to avoid multiple calls. Both can coexist.
Node.js, Spring Boot or Python for my backend?
Spring Boot suits enterprise systems with Java teams and requirements for robustness and integration. Node.js is efficient for real-time APIs and teams already using TypeScript. Python is the natural choice when the backend relies on data processing or AI. We adapt the choice to your existing setup.
How do you secure an API?
With authentication suited to the use case (OAuth 2.0, JWT, API keys), server-side authorization checks, systematic input validation, rate limiting, encrypted exchanges and logging that can be used in case of an incident.
Can you take over and document an existing API?
Yes. We reverse-document the endpoints, add tests to freeze current behaviour, then fix and evolve the API without breaking existing consumers.
How long does API development take?
A focused backend for an application can be delivered in a few weeks. An API platform open to partners, with access management, quotas and a sandbox, usually takes several months.
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Tell us about your project
Describe your need in a few lines: we come back to you with a first analysis and the next steps.