diff --git a/backend/mcp.go b/backend/mcp.go
index a07f394..66ec55a 100644
--- a/backend/mcp.go
+++ b/backend/mcp.go
@@ -254,6 +254,31 @@ func mcpToolDefs() []infra.MCPToolDef {
 				"required": []string{"id"},
 			}),
 		},
+		{
+			Name:        "add_comment",
+			Description: "Anade un comentario (card_message) a una tarjeta. Requiere card_id, body y autor (author_id o author_username). Devuelve el CardMessage creado.",
+			InputSchema: rawSchema(map[string]any{
+				"type": "object",
+				"properties": map[string]any{
+					"card_id":         map[string]any{"type": "string"},
+					"body":            map[string]any{"type": "string"},
+					"author_id":       map[string]any{"type": "string"},
+					"author_username": map[string]any{"type": "string"},
+				},
+				"required": []string{"card_id", "body"},
+			}),
+		},
+		{
+			Name:        "list_comments",
+			Description: "Lista los comentarios (card_messages) de una tarjeta en orden cronologico.",
+			InputSchema: rawSchema(map[string]any{
+				"type": "object",
+				"properties": map[string]any{
+					"card_id": map[string]any{"type": "string"},
+				},
+				"required": []string{"card_id"},
+			}),
+		},
 	}
 }
 
diff --git a/backend/tools.go b/backend/tools.go
index 68d6896..d5f957b 100644
--- a/backend/tools.go
+++ b/backend/tools.go
@@ -50,6 +50,10 @@ func executeTool(db *DB, name string, input json.RawMessage) ToolResult {
 		return toolListUsers(db)
 	case "assign_card":
 		return toolAssignCard(db, input)
+	case "add_comment":
+		return toolAddComment(db, input)
+	case "list_comments":
+		return toolListComments(db, input)
 	default:
 		return errMsg("unknown tool: " + name)
 	}
@@ -59,7 +63,8 @@ func executeTool(db *DB, name string, input json.RawMessage) ToolResult {
 func toolMutates(name string) bool {
 	switch name {
 	case "create_column", "update_column", "rename_column", "delete_column", "reorder_columns",
-		"create_card", "update_card", "delete_card", "move_card", "assign_card":
+		"create_card", "update_card", "delete_card", "move_card", "assign_card",
+		"add_comment":
 		return true
 	}
 	return false
@@ -347,9 +352,66 @@ func validateToolName(name string) error {
 		"update_card": true, "delete_card": true, "move_card": true,
 		"card_history": true, "find_cards": true,
 		"list_users": true, "assign_card": true,
+		"add_comment": true, "list_comments": true,
 	}
 	if !known[name] {
 		return fmt.Errorf("unknown tool: %s", name)
 	}
 	return nil
 }
+
+// toolAddComment appends a comment (card_message) to a card. Accepts either
+// {card_id, body, author_id} or {card_id, body, author_username}. Resolves
+// the username to an id when needed.
+func toolAddComment(db *DB, input json.RawMessage) ToolResult {
+	var in struct {
+		CardID         string `json:"card_id"`
+		Body           string `json:"body"`
+		AuthorID       string `json:"author_id"`
+		AuthorUsername string `json:"author_username"`
+	}
+	if err := json.Unmarshal(input, &in); err != nil {
+		return errResult(err)
+	}
+	if in.CardID == "" {
+		return errMsg("card_id required")
+	}
+	if strings.TrimSpace(in.Body) == "" {
+		return errMsg("body required")
+	}
+	authorID := strings.TrimSpace(in.AuthorID)
+	if authorID == "" {
+		if in.AuthorUsername == "" {
+			return errMsg("author_id or author_username required")
+		}
+		u, _, err := db.GetUserByUsername(in.AuthorUsername)
+		if err != nil {
+			return errResult(fmt.Errorf("author_username: %w", err))
+		}
+		authorID = u.ID
+	}
+	m, err := db.CreateCardMessage(in.CardID, authorID, in.Body)
+	if err != nil {
+		return errResult(err)
+	}
+	return okResult(m)
+}
+
+// toolListComments returns every comment (card_message) attached to a card
+// sorted by created_at ascending.
+func toolListComments(db *DB, input json.RawMessage) ToolResult {
+	var in struct {
+		CardID string `json:"card_id"`
+	}
+	if err := json.Unmarshal(input, &in); err != nil {
+		return errResult(err)
+	}
+	if in.CardID == "" {
+		return errMsg("card_id required")
+	}
+	msgs, err := db.ListCardMessages(in.CardID)
+	if err != nil {
+		return errResult(err)
+	}
+	return okResult(msgs)
+}