Simon Willison: 'Pasted File Editor' — Replicates Claude.ai's File Attachment UX as Open-Source Web Tool

simonwillison.net·low signal

On June 2, Willison published a new tool that mimics Claude.ai's automatic detection of large text pastes and conversion to file attachments. Users can paste text, open files directly, or drag files onto a textarea. Built with Codex desktop assistance, the tool demonstrates Willison's ongoing pattern of extracting useful AI UX patterns into standalone open-source utilities. A small but telling example of how AI-native UX conventions are being disaggregated from proprietary platforms.