Work with Letter.md through WebMCP

Let compatible browser agents read the current page, find documents and Assets, and prepare reviewable work with page-scoped permissions.

Letter.md now exposes page-scoped tools to browsers that support WebMCP, without requiring a separate remote MCP connection.

What changed

Read the current Markdown, document outline, or selected text.
Find and open documents, inspect referenced Assets, and search the Asset library.
Create a document or prepare a reviewable suggestion only after an explicit confirmation.
Match available tools to the active Workspace membership and document role.
Keep direct body edits, deletion, sharing, and publishing outside the WebMCP tool set.

Browsers without WebMCP continue to use Letter.md normally.