Rueil-Malmaison · Paris · Paris region
Bespoke web applications in Paris and Rueil-Malmaison: the business tool that replaces your spreadsheets and your retyping
Client portal, online booking, quotes, member area, dashboard: we build bespoke web applications for trades, shops, professional practices and firms of 3 to 30 people, connected to the tools you already use.
- A fixed price written after the consultation
- Lead time written into the quote
- You own the code
Free · No commitment · An answer within 24 hours
- clients supported
- 150+
- from 14 reviews
- 4.5/5
- for a written answer
- 24 h
Client area
ExampleOpen cases
New quote- Appointments this week
- 12
- Quotes awaiting reply
- 4
- Cases closed this month
- 31
- Kitchen refit · Mrs MartinQuote sent
- Garage extension · Mr PetitVisit booked
- Loft insulation · Mrs RouxIn progress
- Roof repair · Mr BernardCompleted
4 cases shown · See all cases
Free diagnostic
Do you need a web application?
Twelve questions about the way you actually work: the time spent retyping, the tools you use, your volume and the state of your data. The score tells you whether an application is justified or whether a few settings would do.
- A score out of 100 and the detail per axis: time lost, current tools, volume and team, data
- A clear opinion: a bespoke application, automating what you have, or simply a website
- The full report by email, with the 12-section project brief template as a bonus
Free diagnostic · 12 questions · 2 minutes
Your result appears straight away, with no email needed.
- A score out of 100 and the detail per axis: time lost, current tools, volume and team, data
- A clear opinion: a bespoke application, automating what you have, or simply a website
- The full report by email, with the 12-section project brief template as a bonus
Who it is for, and for what problem
When a website is no longer enough: six web applications we build
A bespoke web application puts data to work, it does not simply present your business. These are the six shapes it most often takes with our clients.
- 01
Client portal
Your clients follow their case, upload their documents and look at their invoices without ringing you.
For: Professional practices, agencies, property managers, B2B suppliers
- 02
Booking and appointments
An online diary tied to your real schedule, with confirmation, an automatic reminder and a deposit if you want one.
For: Salons, practitioners, workshops, hire businesses, restaurants
- 03
Online quotes and configurator
The visitor picks their options, gets an estimate, and you receive a complete enquiry, ready to turn into a quote.
For: Trades, joiners, printers, anyone selling with options
- 04
Member area and training
Members-only content, videos, course paths and progress tracking, all reached with an account.
For: Trainers, coaches, associations, clubs
- 05
Business dashboard
Job scheduling, stock, client records, follow-ups: one screen for the whole team, at the office and on site.
For: Firms of 3 to 30 people, building trades, shops
- 06
An in-house tool connected to your software
The application reads from and writes to your diary, your invoicing, your CRM or your email, with nothing retyped.
For: Any business juggling several tools
Often the application is a module added to your site. If you are starting from scratch, begin by pricing up your website in two minutes, then we price the module together.
We see clients in Rueil-Malmaison (92) and work by video call across the whole Paris region: see our web agency in Paris and our web agency in Rueil-Malmaison.
What we see
Three signs that a bespoke web application would save you time
The situations we come across most often at the consultation.
Your spreadsheets are doing a software's job
A shared file, versions crossing over, a formula broken on a Friday evening. With three people it holds. Beyond that, everyone is checking everyone else's work.
Off-the-shelf software does not fit your trade
You pay for four or five subscriptions, each of them does part of the job, and you retype the rest by hand.
Enquiries get lost between your website and your tools
A quote asked for in the evening, an appointment booked by message, a deposit to chase: with no link between your site and the way you work, clients are left waiting.
What you get
What does a web application delivered by ConvertiLab contain?
Here is what the quote covers.
An application you can reach anywhere
From a browser, on a computer, a tablet or a phone, with nothing to install.
Accounts and roles
You, your staff, your clients: each person sees only what concerns them.
Your data in a database in your name
Hosted in Europe, backed up, and exportable at any time in a readable format.
A connection to the tools you use today
Google or Outlook calendar, invoicing, CRM, email, online payment.
The automations worth having
Confirmations, reminders, follow-ups, notifications. With our CRM pillar and its AI integration when something has to be read or written.
Screens drawn for your trade
Mock-ups approved before any development, designed to be quick to use on a phone.
Training for your team
A hands-on session, a short guide, and an answer within 24 hours for the first few weeks.
The source code and every access
Code repository, hosting, domain name and database in your name from the day it goes live.
Reading emails, replying to quote requests, writing copy: our AI integration takes care of it with Claude, following your rules and your tone of voice.
How many hours a week disappear into retyping?
That is the first thing we measure in the free 30 minute consultation, with a straight opinion at the end of it.
How we work
How do we build your bespoke web application?
Five markers in time, always in the same order.
Day 1
Étape 1 : A free 30 minute consultation
You show us how you work today: the files, the emails, the things retyped. We list what the application has to do. If software that already exists would do the job, we say so.
Week 1
Étape 2 : A short brief, mock-ups and a quote
A few pages, the main screens mocked up, a fixed price per phase and a written lead time. Nothing is coded before you approve it.
Phase 1
Étape 3 : A first version you can use
We build the flow that costs you the most time first. You test it with real data, then we add the rest.
Going live
Étape 4 : Training and handover of the accesses
The application live in your name, your team trained, the code and the accesses handed over. The fixes that follow the launch are included.
Every month, if you want it
Étape 5 : Support and new features
Updates, backups, new features. Optional, on quotation, with no minimum term.
What you can check
Applications you can open, and sites where you can try the journeys yourself
We publish no productivity gain and no revenue figure that we cannot prove. Our own web applications, which we run every day, are our first piece of evidence.
With our clients the application is often a module built into the site: a guided quote, a client area, online booking. The three sites below are there to look at.
Quotations taken word for word from our case studies, and no revenue figure published.
Our own applications
What you can open right now
- MerciAvis, NFC plaques and cards for Google reviews (opens in a new tab)
NFC and QR cards on the counter, a dashboard, follow-ups: a web application we designed and that we run ourselves.
- An SEO check in 60 seconds
The free tool on this site analyses an address and returns a report: a web application, not a page.
JSM Jardinage
Brochure website with a four-step guided quote request
“Since launching my site with ConvertiLab, I have taken on more staff to keep up with demand.” The four-step quote journey can be tried out on the site.
Funestore
B2B e-commerce with a reserved client area
A trade catalogue, online ordering and an area reserved for clients in the funeral sector.
La Chasseuse d'Émotions
Portfolio website with online booking
Galleries, how a session works, detailed prices and online booking.
Straight talking
We would rather say no than have you build a tool you do not need
A bespoke application is not always the right answer.
This is for you if...
- Your team retypes the same information into several tools.
- Your clients ring you for information they could look up themselves.
- You follow a precise process that no off-the-shelf software reproduces.
- Someone on your side can spend an hour a week testing the screens.
This is not for you if...
- Software that already exists covers your need: we will tell you so at the consultation.
- You are looking for a native mobile app to publish on the App Store or Google Play.
- You want fifty features in the first version: we always start with a single flow.
- Nobody on your side will be able to test the screens during the project.
Our commitment, in black and white
A fixed price per phase and a lead time written into the quote, with no extra charge along the way. Hosting and monthly support are optional and priced separately.
The code, the data and the accesses are in your name from the day it goes live. If software that already exists would do the job, we say so.
Price and commitment
How much does a bespoke web application cost?
There is no single price: a booking module and a client portal are not the same piece of work. Every quote is written at a fixed price per phase.
- A 30 minute consultation
- FreeBy video call or in Rueil-Malmaison (92), with a straight opinion at the end of it.
- Bespoke web application
- On requestA fixed price per phase, given after the consultation, with the lead time in the quote.
- Support and new features
- Optional, on quotationUpdates, backups, new features. With no minimum term.
What we commit to
- A fixed price per phase, written down before we start, with no extra charge along the way
- A lead time written into the quote, phase by phase
- The source code, the database and the accesses in your name
- Training for your team and fixes after the launch included
- One point of contact, the founder, from the consultation to going live
VAT not applicable, article 293 B of the French tax code. The quote is written and approved before a single line of code.
FAQ
Your questions about building a bespoke web application
What is the difference between a website and a web application?
A website presents your business and brings in enquiries. A web application puts data to work: user accounts, cases, bookings, quotes, dashboards. It is used from a browser, with nothing to install, by your team and by your clients. Often it takes the shape of a module added to the site you already have.
How much does a bespoke web application cost?
The price depends on the number of screens, the user roles and the connections to your tools. We do not publish a single price: a booking module and a full client portal have very little in common. After the free consultation you receive a quote at a fixed price per phase, with the lead time written in. You only pay for the phases you approve.
How long does it take to build a web application?
The lead time is written into the quote. A module built into your site, such as a guided quote request or online booking, is delivered in a few weeks. A portal with several roles and connections to your software is delivered in usable phases, over several months. You use the first version without waiting for the last.
Who owns the application, the code and the data?
You do. The code repository, the hosting, the domain name and the database are all created in your name, and you receive every access when it goes live. You can hand the future work to whoever you like, with no dependence on us.
Which technologies do you use?
React and Next.js for the screens, TypeScript, a PostgreSQL database and hosting in Europe. These are the technologies behind this site and behind our own tools, chosen because they are widespread: any developer can pick the project up after us.
Do I have to give up the software I use today?
No. We connect the application to what you already use: Google or Outlook calendar, your invoicing package, your CRM, your mailbox, online payment. The application replaces the retyping and the spreadsheets, not the tools that work.
Is my data, and my clients' data, protected?
Every user has an account and sees only what concerns them. Traffic is encrypted, the database is backed up and hosted in Europe, and from the brief onwards we plan for what the GDPR requires: consent, how long data is kept, and export and deletion on request.
What if I need new features after delivery?
That is expected. The application is built phase by phase, and every new feature gets a short quote of its own. You can also take optional monthly support for updates and small changes, with no minimum term.
Can you add an application to my existing website?
Yes, if your site allows it technically. Online booking, a guided quote or a client area can often be added to a site that is already there. If the site is too old, we will suggest rebuilding it at the same time, with a separate quote for each part.
The website creation pillar
The other packages in our website creation pillar
An application is often added to a site, or built alongside one. The four other packages in the pillar, with their fixed price and their lead time.
Our other pillars
Our three other pillars for finding your clients
Advertising, search optimisation and CRM plug naturally into an application that runs well.
- 02
Online advertising
Campaigns that cost less than they bring in
Google Ads, Meta Ads (Facebook, Instagram), TikTok, Pinterest and LinkedIn Ads.
On request
Google Ads, Meta Ads and social ads agency in Paris - 03
SEO and AI visibility
Be found on Google, and quoted by AI
Organic search, local SEO (Google Business Profile, customer reviews) and visibility in ChatGPT, Perplexity and Google AI Overviews.
From €500 a month
SEO agency in Rueil-Malmaison and Paris: organic, local, AI - 04
CRM and automatic follow-ups
Every enquiry tracked, followed up and turned into a customer
We set up your CRM, whichever one it is (HubSpot, Salesforce, Pipedrive, Zoho, Brevo, Sellsy, Axonaut, monday CRM or the one you already have), with your website forms and your campaigns connected to it, and automatic follow-ups by email.
On request
CRM and automatic follow-ups for small and medium businesses: HubSpot, Salesforce, Pipedrive
Guides for doing it yourself
Articles on the subject
How much does a website cost in 2026: real prices by type of site?
Website prices range from 300€ to 50,000€ depending on the project. Real prices by type of site (brochure, landing page, e-commerce), the factors that push the price up and the hidden costs to plan for, with ConvertiLab's own prices in the open.
Read the article
What is a brochure website and what is it for?
A full definition of the brochure website, how it differs from an e-commerce site, what it should contain, what it costs and which businesses it suits best.
Read the article
How to create a landing page that really converts visitors into customers?
Most landing pages convert fewer than 3% of their visitors. CTA, copywriting, social proof, speed: the 4 levers that take a page from 2% to 10-15% conversion, with concrete examples.
Read the articleFree consultation
Tell us about your web application project
One question first, your contact details afterwards. A written answer within 24 hours.
What kind of application are you interested in?
No contact details asked for at this step.
A web application project, or a question about the price?
Book 30 minutes, free of charge, and you speak to the founder.