Paint.NET's maintainer says Claude wrote 180,000 lines

Rick Brewster says Claude wrote 180,000 lines of Paint.NET's new Direct2D engine, built from scratch after WINE's version fell short, per Simon Willison's post about Brewster's account.

He puts the total codebase at 700,000 lines, so the agent-written share comes to about a quarter of an app he's maintained for two decades. He calls the result vibe coded and largely untested, and says he corrected resource management and architectural problems by hand.

A similar ratio showed up in a different rewrite. The author behind the Rune text editor converted 65,000 lines of Go into 60,000 lines of Rust for about $650 total, according to his account of the rewrite. He skipped line-by-line translation, extracting the Go into intermediate representations first, hierarchical state machines and graphs, then generating Rust from those. He checked the result with fuzzing and differential testing, replaying terminal sequences and comparing Playwright screenshots against the old binary. A Hacker News commenter asked the obvious question: how do you confirm semantic equivalence across 65,000 lines you never read?

Neither author dodges that question. Neither has an answer for the maintenance year, when a bug report arrives against code no human has read. A new audit of production APIs found that constraints written only in prose, never encoded in a schema, failed silently in 44 of 61 commercial endpoints. Machine-checkable constraints threw an honest error in all 111 tested. The API audit and Brewster's account point at the same failure mode: agent-written code doesn't throw an error when it's wrong, and a test suite is bad at catching that.

Brewster's 180,000-to-520,000 split is probably close to the safe ceiling for code you intend to maintain for a decade. Not because an agent can't write more, but because the human-reviewed share is what you debug from once the rest misbehaves.