What probably matters to youSection of the release
What
Claude Code adds a new hook event type, prompt.attachment, that plugins can implement to inspect and change text attached to a user's message. A hook can rewrite the attachment's text or leave it out entirely before it reaches the model. Claude Code logs what changed and which plugin or hook made the change, including whether the origin was the plugin, a hook, or the engine's own default handling.
Why
This lets plugins control what attachment content actually gets sent to the model, for example filtering or transforming pasted content before use, with a record of what was changed and by what.
The entry above is what we published on the day. These lines were added later, as Anthropic's own pages caught up, and they sit beside the original rather than replacing it.
Confirmed sinceAnthropic's documentation has since written up prompt.attachment, on Mods reference.| `prompt.attachment` | Claude Code adds a message of its own for Claude, such as a reminder. `e.type` names the kind, and for the kinds the types declare, `e.detail` holds the facts the text was written from. | `{ text }`, or `{ text: nul…plugins/mods/referencesee the edit
How sure we are
One source agreesOne thing we can check says the same as this entry.
Anthropic's documentation agreesAnthropic's documentation has since written up prompt.attachment, on Mods reference.
