The Trello MCP connector (connected via Claude) exposes add_comment and add_member as documented actions of the trelloWriteCard tool. However, both actions are rejected server-side with an “Invalid enum value” error as soon as they are actually invoked. Other actions of the same tool (create, update, move, archive, mark_done, attach_label, detach_label) work fine.
Expected behavior: add_comment adds a comment to the card, add_member assigns a member to it, as documented in the tool description.
Actual behavior: both actions fail with “Invalid enum value”.
Reproduced: across multiple sessions, after restarting the desktop app, after an app update, and in the mobile app - the error has persisted consistently since at least 2026-09-23 (add_comment was confirmed working as recently as 2026-09-08, on comments added to a card via the same Trello account).
Impact: automated comment/assignment workflows via the MCP connector are currently not possible; a manual workaround via the Trello web interface is in use instead.
I can’t fix the connector side, but “Invalid enum value” is the wording a Zod schema check produces, so it looks like the tool description still lists those two actions while the validator on the server no longer accepts them. That’s something only Atlassian can change.
If you need comments and assignments working in the meantime, the plain REST API still does both. I just ran these against a test board with an API key and token from Trello
# add a comment
curl -X POST "https://api.trello.com/1/cards/{cardId}/actions/comments?text=Your%20comment&key=KEY&token=TOKEN"
# add a member (the member id, not the username)
curl -X POST "https://api.trello.com/1/cards/{cardId}/idMembers?value={memberId}&key=KEY&token=TOKEN"
The first returns the new commentCard action, the second returns the card’s member list. You can get a member id from GET /1/members/{username}. Docs: https://developer.atlassian.com/cloud/trello/rest/api-group-cards/#api-cards-id-actions-comments-post
If your automation runs somewhere you can make HTTP calls, that keeps it going until the MCP schema is fixed.