Curl: The Forgotten Multiparadigm Programming Language for the World Wide Web
When talking about modern web development today, names like React, Flutter, or perhaps Blazor usually come up. Hardly anyone remembers Curl anymore — a programming language that was already attempting things at the end of the 1990s that seem completely normal today.
And that’s precisely why Curl is actually quite interesting.
Why an article about a “dead” programming language?
I was cleaning out my bookshelf and, as always, getting annoyed about all the technical books I’ve never read. But does “Now I’m Programming Curl” belong in that pile? Yes, and yet I can’t throw it away. As an application developer, I always feel that every programming language can teach you something.
However, as a living programmer, you should probably learn the more important languages first—the ones that still offer jobs and money, like Python, C#, Java, etc. But whoever understands or recognizes the beginnings of Curl sees these approaches in Electron and Co.
What was or is Curl anyway?
Curl was developed by the Curl Corporation. The idea behind it was remarkably ambitious at the time: a single language should simultaneously be:
- HTML replacement
- GUI framework
- Scripting language
- Backend logic
- Interactive web platform
Basically what today consists of multiple technologies. Back then, websites mostly consisted of relatively static HTML with some JavaScript. Curl, on the other hand, wanted to enable complete applications directly in the browser, with complex interfaces, network functions, and proper programming logic.
The whole thing ran through its own runtime or browser plugin.
The concept behind Curl
The language combined declarative UI with object-oriented programming. This allowed you to assemble interfaces and logic relatively compactly.
A small example looked something like this:
{Curl 7.0 applet}
{value
let text-field:TextField =
{TextField width=200}
{VBox
spacing = 10pt,
{text Gib Deinen Namen ein:},
text-field,
{CommandButton
label = "Hallo",
{on Action do
{popup-message
"Hallo " & text-field.value
}
}
}
}
}Today it looks a bit like a mix of:
- XML-UI
- JavaScript
- Desktop GUI toolkit
And much of it reminds you surprisingly strongly of modern frameworks.
Curl was ahead of its time
This is probably the most exciting point. Many ideas that are completely normal today were already present in Curl:
- component-based interfaces
- interactive web apps
- declarative UI
- strong GUI integration
- network and UI logic in one language
- desktop-like applications in the browser
In a way, Curl was an early predecessor of:
- React
- Flutter
- Electron
- Blazor
Why Curl probably disappeared
The language had technically interesting approaches, but never really caught on. There were several reasons for this:
- own browser plugin required
- proprietary platform
- small community
- hardly any open-source ecosystem
- JavaScript became increasingly better
- modern browsers standardized many features
I also focused more on JavaScript back then. By the time AJAX came along, fast JavaScript engines, and later frameworks like React, Curl’s advantage had virtually vanished.
Today the language still exists, but only plays a role in some enterprise and specialized systems, particularly in older enterprise applications.
Frequently Asked Questions (FAQ) about Curl
Based on the official FAQs from curl.com, I’ve summarized the most important questions and answers in my own words:
How does Curl differ from other RIA tools like AJAX, .NET, or Flex 2?
Curl was an integrated solution that combined both the user interface and business logic in a single language. While AJAX was only responsible for asynchronous communication and .NET/Flex were limited to specific platforms, Curl offered a cross-platform solution with built-in GUI development.
Do users have to pay for installing and running the Curl Runtime Environment (RTE)?
The Curl RTE was free for end users. Enterprises had to purchase licenses for development and server deployment, but execution on the client side was free, which facilitated distribution.
What is Occasionally Connected Computing (OCC)?
OCC refers to the ability of applications to function both online and offline. Curl supported this concept by providing local data storage and synchronization mechanisms, which was particularly important for enterprise applications.
Why is OCC support important for enterprise applications?
Many enterprise applications must continue to function even with unstable internet connections. OCC allows employees to continue working in the field or during network problems and synchronize later.
How can Curl successfully migrate legacy client/server applications to the web?
Curl offered special tools and frameworks for migrating classic client/server applications. The similar programming philosophy and powerful GUI components made the transition easier than with web-only solutions.
What are the advantages of Curl when migrating to the web?
- Unified development environment: No separation between frontend and backend
- Powerful GUI components: Better user interfaces than pure HTML solutions
- Offline capability: Support for OCC applications
- Fast development: Less code for complex applications
How can I contact other Curl developers?
Curl had an active community with forums, mailing lists, and regular conferences. Today there are still some specialized groups and legacy support networks.
What’s the difference between Curl RTE and Curl IDE?
The Curl Runtime Environment (RTE) was the execution environment for end users, while the Curl Integrated Development Environment (IDE) was the development tool for programmers. The IDE included editor, debugger, and visual design tools.
Can I test Curl without having to buy it?
Yes, Curl offered free trial versions and developer licenses. You could evaluate the language and tools before making a purchase decision.
Which version of Internet Explorer does the Curl RTE work with?
The Curl RTE was compatible with various Internet Explorer versions, most recently with IE 8-11. Support for modern browsers was no longer available.
Current developments and status
The curl.com website shows that Curl hasn’t completely disappeared:
Status: May 2026
- March 31, 2026: Curl RTE 8.0.16 and CDE 8.0.16001 is released
So the language is still being maintained, but only plays a role in some areas.
Should you take a look at Curl today?
The honest answer is: it depends on why.
Yes, if you …
- are interested in programming languages
- find old web technologies fascinating
- want to see which ideas existed early on
- want to analyze historical concepts
Then Curl can actually be quite interesting. In the end, you lose some time, but learn a few things.
Most of all, you quickly realize that many “modern” ideas aren’t really all that modern.
Rather no, if you …
- are looking for a new language for projects
- want to find jobs with it
- expect a current ecosystem
- need modern libraries and community
Then Curl today is more of a dead end.
The language has hardly any relevance in current development work.
Waste of time or fascinating tech history?
Maybe neither. Curl is no longer a language you need to learn productively. But it’s a good example of how some technologies simply come too early.
Many concepts were clever. Some even surprisingly modern. But Curl relied on a closed plugin model, while the open web continued to evolve.
And that’s precisely why Curl today is more of an interesting piece of web history than a real future technology.
Technical details and concepts
Multiparadigm approach
Curl supported multiple programming paradigms:
- Declarative programming: for UI definitions
- Object-oriented programming: for complex application logic
- Functional programming: for data processing
- Procedural programming: for simple scripts
Rich Internet Applications (RIA)
Curl was one of the pioneers in the RIA field and offered:
- Rich GUI Components: complex UI elements
- Data Binding: automatic synchronization of data and UI
- Network Operations: integrated network functions
- Local Storage: local data storage
- Graphics Support: built-in graphics functions
Enterprise features
Particularly in the enterprise environment, Curl offered important features:
- Security: integrated security concepts
- Scalability: support for large applications
- Integration: connection to existing systems
- Performance: optimized execution
Curl impressively demonstrates how visionary some technology concepts were. Many ideas that are considered “modern” today were already developed in the 1990s. The failure of Curl was less due to technical shortcomings than to strategic factors: the closed ecosystem, dependence on browser plugins, and the rise of open web standards. For programmers interested in the history of web development, Curl is a fascinating example of how the future sometimes comes earlier than the market is ready for it.
The article and my Curl journey are not over here, I think I will take another look at my Curl book after all!
Further links
Recommended literature: Programming languages without Curl book ;)
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