Four modern coding agents (Gemini 3.8 Flash, GPT Astra 6, Opus 5 and Fable 5) were each given a $100 budget and told to build an open-source PDF editor. All produced web apps (mostly pdf.js-based) with basic editing: image insertion, signatures, comments, shapes, redaction and page reordering, but ambition and polish varied - Opus alone attempted editing embedded text, Fable shipped a very minimal highlighter, and several features common in commercial editors (OCR, vector manipulation, robust image handling, multi-selection) were missing. Usability mistakes were frequent and concrete: Gemini placed inserted images by clicking without previews or selection handles, Astra labeled every button with verbose text instead of leveraging standard iconography, apps lacked settings search, many UI controls broke on mobile, and performance regressions appeared from sequential slow backend requests. Numerous bugs persisted (skewed exported images, dark-mode color inversion, unexpected font changes, missing rotations) and none of the projects provided easy native installation or a built-in bug-reporting link.
The core argument is that these failures stem from how agents interact with software: they don’t pursue human-like, purpose-driven workflows, don’t experience friction or impatience that would expose UX flaws, and operate on static snapshots rather than real-time interaction. Because agents miss the small, iterative annoyances that shape usable interfaces, human oversight remains essential - especially for polishing UX and catching edge-case bugs - so open-source software driven by agents will likely remain “sloppy” without a human product-manager role.
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