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Instead of replacing software that works, you can add a custom module that exchanges data with it: client portal, field app, dashboard. Allow $6,800 to $22,400 (€6,000–€20,000)excl. VAT depending on the module and how hard the connection is, which mostly depends on the existing software’s API.
Your ERP or business software does its job well on the essentials, but one piece is missing: access for your customers, an app for your field teams, a readable dashboard. Replacing it entirely would be long, costly and risky. The most sensible alternative is often to extend it with a custom module that talks to it.
The principle: a satellite module
The existing software remains the reference for its data: customers, products, orders, invoices. The custom module connects to it, reads what it needs, and sends back what it produces. For users, it is one more tool, but designed exactly for how they work. For management, it is a limited investment that leaves what works untouched.
This approach has three benefits:
- no heavy migration: the data stays where it is;
- controlled risk: if the module has a problem, the main software keeps running;
- a targeted budget: you pay for the missing piece, not for rewriting what exists.
It is also a way to prepare for the future: if you ever decide to replace the main software, the module stays in place and only needs to be reconnected to the new system.
The most common use cases
| Module | What it does | Data exchanged |
|---|---|---|
| Client portal or extranet | Customers view orders, invoices and documents, and place orders | Customers, orders, invoices, stock |
| Field app | Technicians or sales reps record reports, photos and signatures, even offline | Customers, jobs, products |
| Order taking | Sales reps place orders at the customer’s site, with up-to-date prices | Catalog, prices, orders |
| Dashboard | Management tracks its KPIs without exporting to a spreadsheet | Sales, margins, stock, receivables |
| Automation | A repetitive task (processing orders received by email, reminders) is handled automatically | Depends on the process |
The client portal is covered in detail on the client portal page.
The key question: how to connect
Feasibility and cost depend first on the existing software. During scoping, I check:
- whether an API exists, its documentation, its limits and any cost;
- the license terms: some vendors restrict or charge for data access;
- how often data needs to flow: real time, every few minutes, or once a day;
- the direction of the flow: read-only, or writing back into the main software;
- the quality of existing data, which determines how reliable the module will be.
One rule applies in every case: each piece of information has a single source of truth. If customer addresses are managed in the ERP, the portal displays them but does not let anyone edit them on its side, or else it sends the change back to the ERP. Settling these rules upfront avoids the most common problem with connected tools: two versions of the same data that slowly drift apart.
For common software, dedicated pages go through the options, for example connecting a business app to Sage or to Odoo. If it is your own system that needs to open up to partners, see building an API to open your system to partners.
Budget and timelines
The ranges below exclude VAT. They are based on my business app pricing, plus the “connection to other tools” building block ($2,300 (€2,000)excl. VAT in the estimator) for each piece of software to connect.
| Module | Indicative budget | Timeline |
|---|---|---|
| Dashboard connected to one system | $6,800 to $11,200 (€6,000–€10,000)excl. VAT | 1 to 2 months |
| Field app with offline mode | $9,000 to $18,000 (€8,000–€16,000)excl. VAT | 1 to 3 months |
| Client portal with orders and documents | $11,200 to $22,400 (€10,000–€20,000)excl. VAT | 2 to 3 months |
The cost goes up if the software has no API and file exchanges are needed, or if the module has to write to several systems at once. For a first range, use the estimator.
When extending is not the right answer
Adding a module only makes sense if the foundation is sound. I would rather advise replacing the software if:
- it is no longer maintained by its vendor, or runs on a system that no longer receives updates;
- its data is too inconsistent to feed a reliable module;
- you are already stacking several modules around it to make up for its gaps;
- the vendor forbids data access or makes it prohibitively expensive.
Conversely, if the missing piece is covered by an official extension of your software at a reasonable cost, take it: it will be maintained by the vendor.
How the project works
- A 30-minute call to identify the missing piece and the software involved.
- Scoping (1 to 2 weeks): technical check of the connection, module scope, fixed quote.
- Clickable mockups tested by future users, whether customers or field teams.
- Development in batches, starting with the connection, tested on real data.
- Go-live, training, then three months of support.
The module’s code belongs to you once paid in full. My overall approach is described on the business apps page.
Frequently asked questions
What if our software has no API?
There are other routes: scheduled file exports and imports, reading the database directly when the vendor allows it, or connectors offered by partners. They are less convenient than an API and are checked during scoping, before any commitment.
Can our software vendor object?
Some licenses restrict access to the database or the API, or charge for it. I recommend checking your contract terms and, if needed, asking the vendor before development. I flag this systematically during scoping.
Will the module keep working when the main software is updated?
Yes, if the connection goes through a documented, stable API, which is designed for exactly that. A direct database connection is more fragile when updates happen. Module maintenance includes adapting to API changes.
Where is the module’s data stored?
The main software remains the reference for its own data. The module only stores what belongs to it (portal accounts, photos, reports) in its own database, hosted in France or the EU, as you prefer.