Story Of Curl

If you are reading this on the internet, there is a near-certainty that curl has touched your data today. Whether you are downloading a software package, calling a REST API, building a microservice, or browsing a modern web application, curl is likely operating quietly behind the scenes.

Today, curl runs on billions of devices. It is found in cars, televisions, routers, printers, spacecraft, smartphones, and servers across every major cloud provider. Yet, despite its monumental ubiquity, it began as a humble hobby project by a single developer trying to solve a very specific, mundane problem: tracking currency exchange rates.

This is the story of curl: how it was born, how it survived decades of technological shifts, and how it evolved into one of the most successful open-source projects in human history.

The Humble Beginnings: HttpGet (1996)

In the mid-1990s, the internet was a wild frontier. The World Wide Web was growing rapidly, and developers needed ways to interact with it programmatically.

In 1996, Daniel Stenberg, a Swedish software developer, was working on a project that required him to fetch currency exchange rates from a web page and automatically convert them into Swedish Kronor for IRC users. To accomplish this, he wrote a command-line tool named HttpGet.

“I wanted a tool that could fetch data from a web server without user interaction. That was the entire vision.” — Daniel Stenberg

HttpGet was simple. It only supported HTTP, and its feature set was remarkably thin. However, it proved that command-line web requests were immensely useful. As Stenberg wanted to support more protocols—specifically Gopher, which was popular at the time—he needed a new name.

Thus, in August 1997, urlget was born.

The Birth of curl (1998)

By March 1998, the project had matured enough to warrant a proper release and a new identity. Stenberg settled on the name curl.

The name is a clever pun:

• c stands for client.
• url represents Uniform Resource Locator.
• Together, it forms c-url (client for URLs), pronounced just like the word curl.

At the same time, Stenberg realized he needed a library version of the tool so other programs could perform network transfers without spawning a separate process. Thus, libcurl was born, laying the foundation for curl’s future integration into countless other software ecosystems.

Early Protocol Support

While HTTP is the undisputed king of the web today, the early internet was much more fragmented. If you wanted to build a versatile transfer tool in the late 90s, you had to speak multiple languages. Early versions of curl quickly added support for:

• DICT (Dictionary Server Protocol)
• FTP (File Transfer Protocol)
• FTPS (FTP over SSL)
• Gopher
• HTTP
• HTTPS
• TELNET

This dedication to supporting diverse protocols—even obscure ones—became one of curl’s defining characteristics.

Engineering Philosophy: Robustness and Portability

What allowed curl to outlive countless other command-line utilities from the 90s? The answer lies in Daniel Stenberg’s uncompromising engineering philosophy and rigorous governance.

1. C89 Compatibility

curl is written in standard C (specifically C89). This guarantees that it can be compiled on virtually any platform, from modern Linux kernels running on high-end server clusters to legacy embedded systems and obscure operating systems from decades past.

2. Zero Unnecessary Dependencies

To run curl, you don’t need a massive runtime environment. It has minimal dependencies, relying primarily on standard operating system sockets and optional TLS libraries (like OpenSSL, GnuTLS, or WolfSSL) for secure communication.

3. Backward Compatibility

Perhaps curl’s greatest superpower is its commitment to backward compatibility. Stenberg and the core maintainers adhere strictly to a philosophy where commands and scripts written for curl decades ago should still work identically today. Breaking changes are treated as catastrophic bugs.

# A curl command written in 1999 often looks identical to one written today
curl -O http://example.com/file.zip

The Architecture of libcurl

While millions of users know curl as a command-line utility, its real superpower is libcurl. libcurl is a free, easy-to-use client-side URL transfer library that supports an astonishing array of features:

• Asynchronous and synchronous transfers
• Connection reuse and pipelining
• HTTP/1.1, HTTP/2, and HTTP/3 support
• Proxy support (SOCKS4, SOCKS5, HTTP proxies)
• Cookie management and authentication (Basic, Digest, NTLM, Kerberos, OAuth)
• TLS/SSL certificate verification

Because libcurl is written in C with bindings available for over 60 programming languages—including Python, PHP, Ruby, Java, and Node.js—it serves as the underlying networking engine for countless software frameworks worldwide.

Surviving the Security Era

As the internet transitioned from unencrypted HTTP to ubiquitous HTTPS, curl became the guardian of secure data transit. Handling encryption, certificate validation, and protocol negotiation is notoriously difficult, and security vulnerabilities are an inevitable reality for low-level networking software.

curl handles security with exceptional transparency and rigor. The project has a clear vulnerability disclosure policy, offers bug bounties funded by sponsors, and conducts regular security audits.

+-------------------------------------------------------------+
|                   Common Use Cases for curl                 |
+-------------------------------------------------------------+
|  1. API Testing & Debugging (GET, POST, PUT, DELETE)        |
|  2. Automated CI/CD Pipelines (Fetching dependencies)       |
|  3. System Administration (Health checks, downloading files)|
|  4. Protocol Experimentation (HTTP/3, WebSockets, gRPC)     |
+-------------------------------------------------------------+

When a CVE (Common Vulnerabilities and Exposures) is discovered, the curl team acts with military precision, releasing patches rapidly and communicating clearly with downstream packagers.

The Modern Era: HTTP/3 and Beyond

Even after more than 25 years of active development, curl shows no signs of slowing down. As internet protocols evolve, curl evolves right alongside them.

Recent milestones include:

• HTTP/2 Support: Bringing multiplexed streams and header compression to the command line.
• HTTP/3 and QUIC Support: Integrating UDP-based transport protocols to reduce latency and improve connection establishment over unreliable mobile networks.
• JSON Parsing Enhancements: Making it easier to work with modern APIs directly from the terminal.

Despite boasting over 300 command-line options, curl remains remarkably fast, lightweight, and reliable.

The Community and Maintainership

Behind curl is one of the healthiest open-source communities in existence. Daniel Stenberg remains the lead developer and project coordinator, steering the project with a steady hand. However, curl is no longer a one-man show.

Thousands of contributors have submitted patches, reported bugs, improved documentation, and translated man pages over the decades. The project operates under a benevolent dictator model backed by clear, meritocratic guidelines and a welcoming attitude toward newcomers.

In 2017, Daniel Stenberg received the prestigious Sten Gustaf Thulin Award for his work on curl, recognizing its massive societal and economic impact.

Conclusion

The story of curl is a masterclass in software engineering. It proves that a focused tool, built with rigorous attention to detail, unwavering commitment to backward compatibility, and a relentless dedication to solving developer pain points, can stand the test of time.

From a tiny Swedish script tracking currency conversions to the invisible glue holding the modern digital world together, curl’s journey is a testament to the power of open source.

Next time you type curl https://api.github.com in your terminal, take a brief moment to appreciate the quarter-century of engineering excellence running quietly beneath your fingertips.