Simon Willison publishes a small file-paste editor prototype built with Codex desktop

Simon Willison published a tool called Pasted File Editor that recreates the large-paste behavior found in Claude’s apps. The prototype keeps the editor text unchanged while turning pasted files or text blocks of 1,000 characters or more into attached files below the editor.

The tool supports file previews, full-file viewing, file removal, drag-and-drop, file selection, clipboard paste, and direct image opening with thumbnails. Willison says he had Codex desktop build the prototype, making it a small but concrete example of agent-assisted developer tooling.

This is a lightweight builder story rather than a major platform story. It is a practical example of AI-assisted tool creation and interface patterns moving from AI chat products into standalone utilities.

Source: Simon Willison, “Pasted File Editor” — https://simonwillison.net/2026/Jun/2/pasted-file-editor/