Combien coute un projet d'integration API ?

Ca depend enormement du contexte. Un connecteur entre deux outils qui ont deja des API correctes, c'est quelques milliers d'euros. Un projet d'integration multi-systemes avec de la synchro bidirectionnelle, de la gestion de conflits et un ERP legacy qui n'expose rien -- la on parle d'un autre budget. Je fais un cadrage gratuit pour estimer ca avant de s'engager.

Combien de temps faut-il pour developper une API ou un connecteur ?

Connecteur simple : 2 a 4 semaines. Projet complet multi-systemes avec webhooks et synchro temps reel : 2 a 3 mois.

Comment est geree la securite des API ?

HTTPS/TLS partout, authentification OAuth2 ou JWT selon le cas, validation stricte des payloads entrants (serializers DRF avec des validators custom), rate limiting, et logs d'acces. Pour les donnees sensibles -- donnees de sante, bancaires -- on ajoute du chiffrement au repos et des ACL granulaires.

Mes systemes actuels n'ont pas d'API. C'est quand meme possible ?

Oui, c'est meme assez courant -- surtout sur les ERP anciens (AS/400, Sage en version on-premise, etc.). On peut lire directement dans la base via ODBC, exploiter des fichiers d'echange CSV/XML/EDI, ou s'appuyer sur des exports existants. L'idee c'est de construire une API REST propre par-dessus, meme si le systeme d'origine n'a jamais ete prevu pour ca.

Assurez-vous la maintenance apres la mise en production ?

Oui, via un contrat de maintenance. Le monitoring est en place des le deploiement -- alertes sur les erreurs 5xx, temps de reponse, taux d'echec des synchros. Et la doc technique permet a votre equipe de reprendre la main si vous preferez internaliser.

Quelle est la difference entre API REST et webhook ?

L'API REST c'est du pull : votre appli demande des donnees quand elle en a besoin (GET /api/commandes/). Le webhook c'est du push : le systeme source envoie une requete POST vers votre serveur quand un evenement se produit. En pratique, sur la plupart des projets on utilise les deux : API pour lire et ecrire a la demande, webhooks pour reagir en temps reel aux evenements.

Combien coute ce type de prestation ?

A partir de 1 500 EUR HT pour une API simple. Pour un systeme complet (auth, paiement, webhooks), comptez 3 000 a 8 000 EUR HT selon la complexite.

API REST Development & System Integration

You have an ERP that doesn't communicate with your CRM, an isolated accounting tool, manual CSV exports. I develop APIs and connectors that circulate your data between all of this.

Are your software applications not communicating with each other?

It's a classic. On one side, we have an ERP, on the other, a CRM, something accounting in the middle -- and nothing communicates. Someone always ends up opening Excel to link the two.

Manual CSV exports, every day, between the ERP and the reporting tool -- sometimes with VBA macros written 8 years ago by someone who is no longer here
Copy-paste errors between the CRM and billing, with the associated input errors
Shared Excel files on a network drive serving as an unofficial database between services
Manual processes that stop when the person managing them is on leave

The true cost is not visible in a budget spreadsheet. It's daily wasted time, silent errors propagating, and accumulated frustration.

What I Build

In fact, I develop REST APIs and connectors that facilitate data flow between your software. The goal: we eliminate manual entries, automate the flows, and give each tool access to the data it needs.

Custom REST API

JSON API with auto-generated OpenAPI/Swagger documentation, auth using OAuth2 or JWT depending on the case, endpoint versioning and integration tests. I generally use DRF generic views with nested serializers — this covers 80% of needs, and for the rest, we do custom work.

Connectors and system integration

Development of API connectors between your tools: ERP, CRM, accounting tools, SaaS platforms, industry-specific software. Each connector is tailored to your tech stack. We don't apply a generic solution.

Webhooks and real-time notifications

Webhooks for reacting to events as they occur -- new order, payment, update of record. This replaces the cron scripts that run every 5 minutes to check if something has changed.

Synchronization and data pipelines

"Bidirectional Synchronization" between systems with conflict and retry management on error. Heavy tasks are handled by Celery/Redis workers in the background -- this avoids blocking HTTP requests.

Ready to move forward?

Free quote within 24 hours, no commitment.

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Projects Realized

Some missions of API integration and API development completed. Details are anonymized.

ERP AS/400 -- Logistics Dashboard

The main part: connecting an IBM i (AS/400) ERP to a web-based tracking dashboard. The AS/400 does not expose anything natively in HTTP, so I built an abstraction layer that reads physical DB2 files via ODBC, transforms the data and exposes it via a Django REST API. The frontend queries this API to display stock and production in near real-time.

API REST AS/400 Django PostgreSQL

3CX Telephony -- Internal CRM

Bidirectional Synchronization between a 3CX telephone system and a custom CRM. 3CX Webhooks to capture incoming calls, customer identification by phone number, injection into CRM history. The most delicate: managing simultaneous calls and duplicates.

Webhook 3CX API Django REST Framework

Accounting -- Reporting

Celery Pipeline extracts accounting entries each night, cleans and aggregates, then injects into an analytical PostgreSQL database. This replaced the daily manual CSV export.

Celery Redis API JSON PostgreSQL

E-commerce order webhooks

Receiving webhooks from an e-commerce platform for each new order. On the server side, a FastAPI endpoint validates the HMAC signature, enqueues the processing, and triggers the chain: preparation, invoicing, client notification. The entire process is idempotent -- if the webhook arrives twice, no new orders are created.

Webhook FastAPI Microservices

Technologies

My usual stack for API development and system integration. The choice depends on the project -- if you already have a stack in place, we can adapt.

API Frameworks

Django REST Framework FastAPI Django Flask

Database & Cache

PostgreSQL Redis SQLite MongoDB

Asynchronous treatment

Celery Redis Queue Webhooks

Security & Standards

OAuth2 JWT OpenAPI / Swagger HTTPS / TLS

Infrastructure

Docker Nginx CI/CD Linux Git

Methodology

How does it work concretely on an API integration project:

Audit and alignment We are looking at what exists -- what systems, what data flows, where it fits best. We identify what has the most value to connect first.
Technical Design Start OpenAPI before writing code. We define the endpoints, data models, authentication, error management. This avoids discovering architecture problems halfway through.
Iterative development Module-by-module construction. Unit tests and integration tests at each step -- classic TDD.
Tests and Validation Load testing (to ensure it holds up when there is volume), security tests, limit case validation with your real data in pre-prod. This is often where edge cases that no one had anticipated are discovered.
Deployment Progressive deployment with monitoring. Rollback is possible.
Documentation and Transfer Generated Doc Swagger/OpenAPI, technical guide, transfer to your team. The goal is for you to be able to maintain the system without me if necessary.

A project integration?

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Frequently Asked Questions

How much does an API integration project cost?

It greatly depends on the context. A connector between two tools that already have correct APIs costs around several thousand euros. A multi-system integration project with bidirectional sync, conflict management, and an ERP legacy system that exposes nothing - we're talking about another budget. I offer a free estimation before committing.

How long does it take to develop an API or a connector?

Simple Connector: 2 to 4 weeks. Complete multi-system project with webhooks and real-time sync: 2 to 3 months.

How is API security managed?

HTTPS/TLS everywhere, authentication with OAuth2 or JWT depending on the case, strict validation of incoming payloads (DRF serializers with custom validators), rate limiting, and access logs. For sensitive data -- health, financial -- we add encryption at rest and granular ACL. The rate limiting is DRF throttling or nginx limit_req depending on whether we want to do it at the application level or infrastructure level.

My current systems don't have an API. Is it still possible?

Yes, it's quite common – especially with older ERP systems (AS/400, on-premise Sage, etc.). You can read directly from the database via ODBC, work with CSV/XML/EDI exchange files, or leverage existing exports. The idea is to build a proprietary REST API on top of it, even if the original system wasn't designed for that.

Ensure maintenance after deployment?

Yes, through a **maintenance contract**. Monitoring is in place from deployment -- alerts for 5xx errors, response time, failure rate of synchronizations. And the technical documentation allows your team to take over if you prefer to internalize.

What is the difference between API REST and webhook?

The REST API is pull-based: your app requests data when needed (GET /api/orders/). The webhook is push-based: the source system sends a POST request to your server when an event occurs. In practice, on most projects, both are used: API for reading and writing on demand, webhooks for reacting in real-time to events.

What is the cost for this type of service?

From 1,500 EUR excluding tax for a simple API. For a complete system (auth, payment, webhooks), expect to pay between 3,000 to 8,000 EUR excluding tax depending on complexity.