Django Co-creator Simon Willison: Claude Code Ran for 12 Hours to Produce a Complete SPARQL Implementation, But I Can’t Review It
Django co-creator and Datasette creator Simon Willison conducted an experiment using Claude Code’s Ultracode mode: he issued a prompt containing a typo, allowing the AI agent to run continuously for over 12 hours, ultimately producing a SPARQL SQLite extension that passed 636 W3C tests. He acknowledged that the codebase had exceeded his capacity for manual review, thereby questioning: if he cannot understand the output, how much value does this achievement hold for him?
Simon Willison sent a prompt to Claude Code’s Ultracode mode with the intention of having the extension "hit the data rows directly," but accidentally typed "delete rows" on his phone. This instruction, containing a typo, caused Claude Code to run continuously for over 12 hours, ultimately producing a complete implementation of SPARQL 1.1—sparqlite, a loadable SQLite extension written in Rust that natively executes SPARQL queries and updates within the SQLite process.
The Ultracode mode works by generating JavaScript to define and coordinate a network of subagents, each handling different parts of complex problems. sparqlite employs integer-encoded terms, covering indexes, a cost-based query planner, batched joins, and an optional direct SQLite B-tree reader; it is 3.5 times faster than SQL translation schemes in count mode and 2.8 times faster when returning full results, passing 636 of the 639 applicable W3C evaluation tests.
When Willison checked on the progress the next day, he found that the AI had built a substantial number of Rust crates, so he added a follow-up prompt requesting that every crate directory include a README, a tutorial.md teaching users how to install the extension and run SPARQL in the SQLite command line, and a script to populate realistic example data. He concluded: "This feels like next-level vibe coding—the produced code is not remotely feasible to review line-by-line, and even following the documentation is a significant investment of work. I now have a full SPARQL implementation inside SQLite, but if I created it on a whim and can't (or won't) invest the necessary time to understand what it can do, how valuable is it to me?"