How to use Claude to reimplement curl in Rust
The author reports that urlx passes 1,300 of 1,300 applicable curl tests and provides a libcurl-compatible C ABI, while some features remain unfinished.
news.ycombinator.com
Prompt to try
Editorial adaptation, not the source author’s exact prompt. Replace bracketed inputs and review tool permissions first.
Reimplement [well-tested project] in [target language], using [existing test suite] as the specification. Iterate by implementing features, running applicable tests and planning next fixes. Analyze unresolved failures, create issues and assign focused fixes to subagents. Report remaining gaps.
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See placements →What happened
The author reports that urlx passes 1,300 of 1,300 applicable curl tests and provides a libcurl-compatible C ABI, while some features remain unfinished.
Reported by jawiggins on Hacker NewsHow the agent did it
- Used the curl test suite as an implementation specification.
- Ran feature implementation, testing and planning loops.
- Directed analysis of remaining failures and creation of issues.
Where a person stepped in
The author later directed failure analysis and subagent assignments; the post does not describe a comprehensive human code review.
A person set the goal and reviewed the result.
Jon Wiggins used Claude Code to develop urlx, a Rust replacement for curl and libcurl. His starting insight came from an earlier libxml2 replacement: a comprehensive existing test suite could serve as the specification for an agent’s implementation work.
Most urlx development happened in two iteration loops lasting approximately sixteen hours each. Claude Code implemented features, ran tests and planned its next work. Toward the end, Wiggins took a more manual role, directing it to analyze remaining failures, create issues and send those issues to teams of subagents for fixes.
The author reports that urlx passed all 1,300 applicable curl tests. The described implementation supports numerous protocols, including HTTP variants, FTP, SFTP, WebSocket and mail protocols. It also includes 261 command-line flags, authentication methods, cookies, HSTS, proxies and a libcurl-compatible C ABI.
Wiggins explicitly says some features remain unfinished and that he does not expect people to replace curl with this project. He presents it as evidence for using established tests to guide rapid reimplementation. Who it's for: developers exploring compatibility projects with a substantial test suite and time to investigate remaining failures.
Prompt
Suggested prompt (written by Agents In Use, not the author's)
Source: Hacker News · jawiggins
Frequently asked questions
What guided the implementation?
The existing curl test suite served as the specification, with repeated feature implementation, test execution and planning.
Does the author recommend replacing curl?
No. The author says they do not expect anyone to replace curl with urlx and acknowledges remaining features.
More details
Remaining steps
- Assigned those issues to teams of subagents for fixes.
About this account
Claude Code repeatedly implemented features, ran tests and planned next steps in long iteration loops.
Platform: Hacker News. Attribution: https://news.ycombinator.com/item?id=47490735. Prompt: Suggested (written by Agents In Use, not the author's). Sourced by the Agents In Use pipeline.
Credit: jawiggins on Hacker News
Source published 23 Mar 2026
Source checked 14 Oct 2026
Tools and topics
Claude Code · curl test suite · Rust
Rust · Compatibility · Test suites
Editorial completeness: 100/100. Measures documented fields, not agent performance or verified outcomes.