The Bun rewrite proves 'never rewrite from scratch' was always a cope
In just 11 days, 64 AI agents successfully ported roughly 535,000 lines of Zig code to Rust. It didn't take 14 months, or a war room full of senior engineers. All it took was eleven days and a credit card. ## The rule that just cracked In the year 2000, Joel Spolsky wrote that the rewrite from scratch is the "single worst strategic mistake" that any software company can make. That became gospel.…
The "Bun rewrite" demonstrates that rewriting software from scratch is not always the best approach, as previously believed. In 2000, Joel Spolsky argued that rewriting a software product from scratch is the "single worst strategic mistake" a company can make due to the loss of bug fixes and encoded knowledge in the existing codebase.
However, the recent case of Bun proves this rule to be a "copew," as it was able to rewrite the core of its runtime from Zig to Rust in just 11 days, with a team of 64 AI agents handling the translation process. This approach resulted in significant improvements in memory usage, bug fixes, and performance, while still introducing some known issues and unsafe Rust code.
The case of Bun highlights the limitations of the "never rewrite from scratch" rule and suggests that in certain situations, a rewrite might be a more efficient solution than maintaining and updating existing code.
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