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Web Development

Custom websites and web applications for businesses that want a website that works just like they do: structured, fast, and scalable.

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Web Development

Every website we build is developed specifically for each project. No themes, no templates, no page builders. We write the code ourselves because that allows us to maintain full control over performance, maintainability, and scalability.

Custom code
instead of templates

Modular design,
expandable at any time

Measurable Performance
From Day One

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Why Custom Web Development Makes a Difference

Pre-made themes and page builders save time at the beginning, but cost more in the long run—in terms of performance, maintenance, and flexibility. We develop every website from the ground up. That means clean code without unnecessary dependencies, clear structures for your editorial team, and a system that grows with your needs. No workarounds that break with the next update. And no reliance on a theme provider who might stop updating tomorrow.

The Right CMS for Your Project

Depending on your needs, we use WordPress, TYPO3, or HubSpot CMS. WordPress is suitable for most corporate websites and offers a backend that editorial teams can quickly get the hang of. TYPO3 is used when multilingual support, complex permission structures, or enterprise-level requirements are needed. HubSpot CMS connects your website directly to CRM and marketing automation. If you’d rather work without a traditional backend, Webflow is another option. We’ll work with you to honestly determine which system is right for your project—even if the answer is sometimes “none of the above.”

Mitarbeiter von seitenweise im Gespräch im Büro in Bielefeld

We don't build websites using templates. Everything we create is developed individually for each project. Here's what we prioritize most in the process.

Frontend-Code mit der dazugehörigen Seitenvorschau

Custom Front-End Development

No themes, no page builders. We code the front end by hand: clean HTML, modular CSS, and JavaScript that does exactly what it’s supposed to. The result is websites that load quickly, work on all devices, and can be expanded.

Backend-Oberfläche einer Webanwendung auf einem Tablet

Well-designed backend architecture

A good backend makes day-to-day work easier. We develop content structures, input forms, and workflows in the CMS so that your team can manage content without needing any technical knowledge.

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API Development and Integrations

Whether it's CRM, ERP, PIM, or applicant tracking: we develop interfaces that connect your website to the systems where your data resides. REST, GraphQL, or custom integrations.

Ladezeit-Messung einer Website auf dem Smartphone

Performance Optimization

Load times under two seconds aren't a bonus—they're the standard. We optimize images, minimize requests, implement caching strategies, and ensure that your Core Web Vitals stay in the green.

Modularer Seitenaufbau aus Hero, Text-Bild-Block, Grid und Call-to-Action

Modular Design

Every website we build consists of reusable components. This makes it easy to add new features, keeps the code maintainable, and provides your editorial team with flexible building blocks for new pages.

Barrierefreie Navigation mit ARIA-Attributen und Screenreader-Ausgabe

Accessibility

The BFSG has been in effect since June 2025. We develop in accordance with WCAG 2.1 guidelines: semantic HTML, keyboard navigation, proper contrast, and a structure that works with screen readers.

These companies know how we work

We write HTML, CSS, and JavaScript by hand. No page builders, no visual editors that generate bloated code. Instead: semantic markup that search engines and screen readers alike can understand. For our styling architecture, we rely on Tailwind CSS, which allows us to implement consistent designs efficiently without accumulating legacy CSS. We develop animations and interactions using GSAP or native JavaScript, depending on the requirements and complexity. Every page is tested on all relevant devices and browsers before it goes live. We check not only the presentation but also load times, interactivity, and visual stability based on the Core Web Vitals. The result: websites that load quickly, work on every screen, and remain stable even as content grows. This is the part that a web development agency should not outsource.

What Our Customers Say

„The team at seitenweise consists of our graphic design and web development professionals. Whenever we need help, they’re always there for us—quickly and reliably. Thank you for the great collaboration!“

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Sandra Meder

Sage

„seitenweise impressed us with fast delivery, friendly communication, and their patience in incorporating our requests! If you want a fast, attractive, and SEO-optimized WordPress website, you should have one built here.“

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Michael Bykovski

Computerra

„Working with an agency requires good ideas, cutting-edge technology, and clear budgets with no surprises. But the personal chemistry has to be right, too. With seitenweise, everything was just right. It was really fun.“

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Mathias Schwaben

Intervideo

„Since we started working with seitenweise, our website has improved significantly. In 2023, they used their extensive expertise to transform our static website into a dynamic WordPress site.“

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Dirk Bockelmann

DFT

Mitarbeiter von seitenweise am Schreibtisch bei der Projektarbeit Mitarbeiter von seitenweise arbeitet konzentriert am Rechner Mitarbeiter von seitenweise arbeitet an einem Kundenprojekt Mitarbeiter von seitenweise am Arbeitsplatz in Bielefeld

From the first meeting to go-live

Mitarbeiter von seitenweise am Schreibtisch bei der Projektarbeit
Mitarbeiter von seitenweise arbeitet konzentriert am Rechner
Mitarbeiter von seitenweise arbeitet an einem Kundenprojekt
Mitarbeiter von seitenweise am Arbeitsplatz in Bielefeld

Understanding Requirements

Together, we’ll clarify what your website or web application is intended to achieve: target audiences, features, content, integrations, and technical requirements. This will result in a concept that includes a site structure, a CMS recommendation, and a technical framework. During this phase, we’ll also define what your team should be able to maintain on its own later on and where fixed structures make more sense. This way, both sides know from the start exactly what the project entails.

Design and Prototype

We develop the visual design based on the concept. You’ll see drafts for the most important page types, provide feedback, and we’ll iterate until we reach the final result. From the very beginning, we consider how the design will be implemented in the CMS. Which elements can your team create, and where are fixed layouts the better choice? This saves time during development.

Development and CMS Setup

We implement the design as clean code and set up the CMS so that your editorial team can work independently. This includes custom content elements, page templates, and a clear backend structure with validations and help texts. If needed, we develop custom features or integrate third-party systems via APIs. Every component is designed with maintainability and scalability in mind.

Testing and Launch

Before the site goes live, we test its features, performance, responsiveness, and accessibility on all common devices and browsers. Your team will receive an introduction to the backend and will be able to enter initial content on their own. Once everything is set up and you give the green light, the site will go live. After that, we’ll remain available for enhancements, new requirements, or ongoing maintenance.

Frequently
Asked
Questions

Well-thought-out

Fast

Kollege stellt dem Team ein Projekt im Besprechungsraum vor

We turn design into technology that works.

seitenweise is a digital agency based in Bielefeld, founded in 1999. With over 100 clients and more than 500 projects, we’ve proven that we build long-term partnerships, not just take on individual projects. Our focus is on custom web development using WordPress, TYPO3, and HubSpot CMS. Every website is built from the ground up—no themes, no templates, and no page builders. Many of our clients are from East Westphalia-Lippe, and many come from much farther away. We also offer strategy, UX/UI design, SEO, and video—all from a single source. Short communication channels, honest advice, and a team that knows your project—not just a ticket number.

Portrait von Marcel Pietsch vor einer Holzlamellenwand

Marcel and André are your points of contact at seitenweise. They're happy to answer any questions you may have about web development.

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Whether it's a new website, a relaunch, or a technical enhancement: tell us where you're at and what you're planning. No strings attached—it'll take just 30 minutes.

Let's go!