Web Application Development
Custom web application development across Europe: portals, SaaS and internal tools built by engineers with a security background. Free scoping quote.
Web application development is what you need when a website is not enough: a customer portal, an internal tool, a booking system, a SaaS product, anything with logins, roles and real business logic behind it. We build those for companies across Europe, and because our other discipline is offensive security, the applications we write are built by people who know exactly how attackers get in.
One thing to be clear about up front. SafetyBis is a European cybersecurity firm, and custom development is a separate practice we run alongside the penetration testing side. Different team, different contracts, different deliverables. What you get from the arrangement is a development shop where the engineers were taught to code by the people who break applications. When your app holds customer data and money moves through it, that background is not a marketing line, it changes what ships.
What web application development actually means here
A brochure site tells people about your business. A web application does the work of your business. The moment you have users who log in, data that belongs to specific people, and rules about who can see and do what, you are in application territory, and the engineering is a different discipline from putting up pages. We build the applications that run operations, not just the ones that describe them.
How we approach a build
We do not disappear for two months and come back with a surprise. Custom web application development works when you can see progress every week and change your mind cheaply while it is still cheap to change. Our process is built around that.
Shape the problem before the solution
Most failed projects failed at the start, not the end. We spend real time on what the application has to do, who uses it, and what the awkward edge cases are, because those edges are where budgets die. You leave discovery with user flows, a data model sketch, and a milestone plan you can hold us to.
Choose a stack that fits, not one that impresses
We are pragmatic about technology. On the back end that usually means PHP with Laravel or Symfony, or Node.js where the workload suits it; on the front end, React or Vue where an app genuinely needs a rich client, and something lighter when it does not. We pick for your team’s ability to maintain it after we hand over, not for what looks good in a conference talk.
Build in vertical slices
Rather than building the whole database, then the whole back end, then the whole UI, we ship one working feature end to end, then the next. You get something clickable early. That is how you catch a misunderstanding in week two instead of week ten, and it is why our estimates tend to hold.
Testing as we go
Automated tests cover the logic that would be expensive to get wrong: authentication, permissions, money, anything that mutates data. Manual QA covers the human experience. Neither is an afterthought bolted on before launch.
Security is designed in, not sprinkled on
This is where a web application development company with a security background earns its keep. The most common serious flaws in custom applications are not exotic. They are broken access control, where one user can reach another user’s data by changing a number in the URL; injection, where user input reaches the database unescaped; and authentication that can be sidestepped. Our engineers know these patterns because our other team exploits them for a living.
Access control that verifies ownership
Every endpoint that returns data checks not just that you are logged in, but that this record is actually yours. That single discipline kills the IDOR bugs that leak one customer’s invoices to another. It is boring to write and it is the thing cheap builds skip.
Input handled as hostile
Anything a user can type or send is treated as an attack until proven otherwise. Queries are parameterised, output is encoded for its context, and file uploads are validated by content rather than filename. This closes the door on SQL injection and stored cross-site scripting before either can reach production.
Where the formal test fits
Building securely and proving it are two different things. If you need documented proof for an enterprise customer or a compliance requirement, our offensive security team runs a full application penetration test against the finished product and produces a report mapped to the OWASP Top 10, with an attestation letter. That is a separate engagement with its own quote. The development work does not commit you to it, and it is priced on its own.
Want this tested on your own systems?
Free 20-minute scoping call, a fixed price with no hourly surprises, and a free retest once you fix what we find.
Working with your existing systems
New applications almost never live alone. They authenticate against your identity provider, pull data from your CRM, push events to your finance system, and take payments through a gateway. Each connection is a contract that has to keep working when the other side changes.
Identity and single sign-on
We integrate OAuth and OpenID Connect, SAML for enterprise SSO, and multi-factor authentication where the data warrants it. Getting login right is not glamorous, and it is the first thing a serious buyer of your product will scrutinise.
APIs and third parties
We build APIs that other systems can actually use: versioned, documented, and rate-limited so one noisy client cannot take the rest down. When we consume someone else’s API, we build it to degrade gracefully, because third parties have outages and your app should survive them.
Rescuing an application in trouble
A good share of our work is not greenfield. It is an app a previous developer or agency left behind: no tests, no documentation, and a login only they understood. We are comfortable there. We start with an audit that maps what the code actually does, flags the security holes and the bus-factor risks, and gives you a prioritised plan. From there we stabilise first and improve second, so the thing keeps running while we fix it.
Data, GDPR and where the application lives
If your application touches personal data, and most do, GDPR is not a box you tick at the end. We build with data protection in mind from the data model up: personal fields are identified early, retention and deletion are actual features rather than promises, and access to sensitive records is logged. That saves you an ugly retrofit later when a customer exercises their right to erasure and you discover the data is scattered across six tables and a log file.
Hosting and deployment
We deploy to the European regions of the major clouds, or to a provider you already use, with backups that are tested rather than merely configured. Deployment is automated so releases are boring and reversible, which matters the first time a change misbehaves in production and you need to roll back in minutes, not hours.
Keeping it running
Applications need care after launch: dependency updates, security patches, and the occasional bug that only shows up at real scale. We can hand the running of it to your team with proper documentation, or stay on for maintenance under a clear arrangement. What we do not do is walk away and leave you guessing.
Web application development pricing
Application projects are scoped, never sold off a menu, because the cost lives in the business logic and the integrations, not the page count. We do not publish day-rates for project work. A real number comes out of the discovery stage, quoted against fixed milestones so you know it before we start.
| Project type | What’s included | Typical timeline | Pricing |
|---|---|---|---|
| Discovery and prototype | User flows, data model, clickable prototype and a costed build plan you can take anywhere | 1–3 weeks | project-scoped, from a free quote |
| MVP build | A focused first version of a product or internal tool: core features, auth, admin, launched to real users | 6–12 weeks | project-scoped, from a free quote |
| Full application | Multi-role platform with integrations, API, reporting and the awkward business rules handled properly | 3–6 months | project-scoped, from a free quote |
| Audit and rescue | Review of an inherited codebase, security and bus-factor findings, and a plan to stabilise and improve it | 1–2 weeks | project-scoped, from a free quote |
| Ongoing development | A steady stream of features and fixes on an app we or someone else built, on a rolling arrangement | rolling | project-scoped, from a free quote |
| Large platform | Multi-tenant SaaS or an estate of internal systems, scoped after a discovery workshop | on scoping | project-scoped, from a free quote |
Every engagement is fixed against agreed milestones and quoted after a free scoping call, with work done under NDA anywhere in Europe, on-site or remote. Scope my project
What you walk away with
An application and its source
You own the repository, the infrastructure setup and the documentation. There is no proprietary layer you have to keep paying us to touch. If you bring in your own team later, they can read what we wrote.
A handover that means something
At launch you get architecture notes, an explanation of the integrations and the deployment, and the list of things to keep an eye on. Whether your team runs it from there or we stay on for ongoing development, you are never dependent on a single person’s memory.
FAQ
How much does custom web application development cost?
What is the best web application development platform to build on?
Can you build just an MVP first?
Will the application be secure?
Can you take over an app another agency built?
Do you handle single sign-on and multi-factor authentication?
How long until I see something working?
Do you sign an NDA?
Related services
Founders and operations leaders who need real software, not a website: a SaaS product, a customer portal, an internal tool, or a rescue of an application a previous team left in a fragile state, built by a team that treats security as part of the job.
Security you can prove
The same standard on every engagement, big or small.
Evidence, not opinions
Every finding ships with a reproduction and proof of concept — no vague "maybe vulnerable".
Humans over scanners
Certified engineers find the logic flaws and chained attacks automated tools walk straight past.
Fixed price, free retest
You know the cost up front, and verifying the fix is part of the deal — not a second invoice.
Ready to lock this down?
Free scoping call, fixed price, free retest. Tell us what you're running and we'll take it from there — usually within one business day.
Tell us what you're running
Scoping is free. We reply within one business day, and under 30 minutes for active incidents.