Curl: The Forgotten Multiparadigm Programming Language for the Web
When people talk about modern web development today, names like React, Flutter, or maybe Blazor come up. But hardly anyone remembers Curl — a programming language that attempted things back in the late 1990s that seem completely normal now.
And that’s exactly what makes Curl pretty interesting.
Why write about a “dead” programming language?
I cleaned out my bookshelf recently, and as usual I felt annoyed at all those technical books I never read. But should “Now I Program Curl” go on the donation pile? Yes and no — I just can’t bring myself to throw it away. As an application developer, I’ve always felt that every programming language has something to teach you.
That said, if you’re actively programming, you probably should learn the more important languages first — the ones that pay the bills, like Python, C#, Java, and so on. But once you understand Curl’s origins or recognize its patterns, you start seeing those same approaches in Electron and similar tools.
What was Curl, anyway?
Curl was developed by the Curl Corporation. The idea behind it was remarkably ambitious: a single language that would simultaneously serve as:
- HTML replacement
- GUI framework
- Scripting language
- Backend logic
- Interactive web platform
Basically, what today requires several different technologies. Back then, most websites consisted of relatively static HTML with a bit of JavaScript. Curl, on the other hand, wanted to enable complete applications to run directly in the browser — with complex interfaces, networking capabilities, and proper programming logic.
It all ran through a proprietary runtime or browser plugin.
The concept behind Curl
The language combined declarative UI with object-oriented programming. This allowed you to build interfaces and logic in a fairly compact way.
A simple example looked something like this:
{Curl 7.0 applet}
{value
let text-field:TextField =
{TextField width=200}
{VBox
spacing = 10pt,
{text Enter your name:},
text-field,
{CommandButton
label = "Hello",
{on Action do
{popup-message
"Hello " & text-field.value
}
}
}
}
}Today it looks a bit like a mix of:
- XML-based UI
- JavaScript
- Desktop GUI toolkit
And it’s surprisingly reminiscent of modern frameworks in many ways.
Curl was ahead of its time
This is probably the most interesting point. Many ideas that are completely normal today were already present in Curl:
- Component-based interfaces
- Interactive web apps
- Declarative UI
- Tight GUI integration
- Network and UI logic in a single language
- Desktop-like applications in the browser
In many ways, Curl was an early precursor to:
- React
- Flutter
- Electron
- Blazor
Why Curl probably disappeared
The language had technically interesting approaches, but it never really gained traction. There were several reasons for this:
- Required a custom browser plugin
- Proprietary platform
- Small community
- Little open-source ecosystem
- JavaScript kept improving
- Modern browsers standardized many features
Back then, I focused more on JavaScript myself. By the time AJAX came around, followed by fast JavaScript engines and later frameworks like React, Curl’s advantages had basically evaporated.
Today the language still exists, but it only plays a role in a few enterprise and specialized systems, particularly in legacy business applications.
Frequently Asked Questions (FAQ) About Curl
Based on the official FAQs from curl.com, I’ve summarized the key 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 only handled asynchronous communication and .NET/Flex were tied 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. Organizations needed to purchase licenses for development and server use, but client-side execution was free, which helped with adoption.
What is Occasionally Connected Computing (OCC)?
OCC refers to the ability of applications to work 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 business applications must continue functioning even with unstable internet connections. OCC allows employees to keep working in the field or during network problems and synchronize later.
How could Curl help migrate legacy client/server applications to the web?
Curl offered specialized tools and frameworks for migrating traditional client/server applications. The similar programming philosophy and powerful GUI components made the transition simpler than with web-only solutions.
What are the benefits of Curl for web migration?
- 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 connect with 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 try 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 Internet Explorer versions does the Curl RTE work with?
The Curl RTE was compatible with various Internet Explorer versions, most recently IE 8-11. Modern browsers no longer received support.
Current developments and status
The curl.com website shows that Curl hasn’t completely disappeared:
As of 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 it only plays a significant role in certain areas.
Should you 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
- Like analyzing historical concepts
Then Curl can actually be quite interesting. You spend some time on it, but you’ll learn a few things along the way.
Most importantly, you’ll quickly realize that many “modern” ideas aren’t actually that modern at all.
Probably not, 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 support
Then Curl today is more of a dead end.
The language has little relevance in current development work.
Wasted time or fascinating tech history?
Maybe neither. Curl isn’t a language you need to learn productively anymore. But it’s a good example of how some technologies just come too early.
Many of its concepts were clever. Some were even surprisingly modern. But Curl relied on a closed plugin model while the open web kept evolving.
And that’s exactly why Curl today is more an interesting piece of web history than a genuine 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 space and offered:
- Rich GUI Components: complex UI elements
- Data Binding: automatic synchronization of data and UI
- Network Operations: integrated networking capabilities
- Local Storage: local data persistence
- Graphics Support: built-in graphics functionality
Enterprise features
Particularly in the business world, Curl provided important capabilities:
- Security: integrated security concepts
- Scalability: support for large applications
- Integration: connection to existing systems
- Performance: optimized execution
Curl demonstrates impressively how visionary some technology concepts were. Many ideas considered “modern” today were already being developed in the 1990s.
Curl’s failure came less from technical shortcomings than from strategic factors: the closed ecosystem, dependence on browser plugins, and the rise of open web standards.
For programmers interested in web development history, Curl is a fascinating example of how the future sometimes arrives before the market is ready for it.
My journey through Curl and this article aren’t quite finished yet — I think I’ll take another look at my Curl book after all!
Further reading
Recommended reading: Programming languages (without the Curl book ;)
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