Agents can now leave comments and suggestions on Google Docs
The Google Docs API finally added support for comments and suggestions.
These were all written by Claude:

I’m doing this via the gdoc CLI, which works with Claude Code or Codex. An MCP port could make it work with Cowork or ChatGPT. Not a developer? Ask your tech team, or wait a few weeks for the consumer apps to enable it...
Proof of concept: here’s the /proofread-doc skill I used for the test above.
