diff --git a/lunatask/habits.go b/lunatask/habits.go
index c979e77eb4b1b490b0dcff4e58ce0ea9e8d7a795..1ad56897d57b0e375ab95a616716132e8b8add7a 100644
--- a/lunatask/habits.go
+++ b/lunatask/habits.go
@@ -8,13 +8,12 @@ import (
 	"context"
 	"fmt"
 	"net/http"
-	"time"
 )
 
 // TrackHabitActivityRequest represents the request to track a habit activity.
 type TrackHabitActivityRequest struct {
-	// PerformedOn is the ISO-8601 date when the activity was performed (e.g., "2024-08-26").
-	PerformedOn string `json:"performed_on"`
+	// PerformedOn is the date when the activity was performed.
+	PerformedOn Date `json:"performed_on"`
 }
 
 // TrackHabitActivityResponse represents the response from Lunatask API when tracking a habit activity.
@@ -29,15 +28,10 @@ func (c *Client) TrackHabitActivity(ctx context.Context, habitID string, request
 	if habitID == "" {
 		return nil, fmt.Errorf("%w: habit ID cannot be empty", ErrBadRequest)
 	}
-	if request.PerformedOn == "" {
+	if request.PerformedOn.IsZero() {
 		return nil, fmt.Errorf("%w: performed_on is required", ErrBadRequest)
 	}
 
-	// Validate date format (YYYY-MM-DD)
-	if _, err := time.Parse("2006-01-02", request.PerformedOn); err != nil {
-		return nil, fmt.Errorf("%w: performed_on must be a valid ISO-8601 date (YYYY-MM-DD)", ErrBadRequest)
-	}
-
 	resp, _, err := doJSON[TrackHabitActivityResponse](c, ctx, http.MethodPost, "/habits/"+habitID+"/track", request)
 	if err != nil {
 		return nil, err
diff --git a/tools/habits.go b/tools/habits.go
index 0dcd93661f2e1976cd1d59755a5f0568dd80d696..cf8719bc327919ce645d7acafd4e5b3f8254f163 100644
--- a/tools/habits.go
+++ b/tools/habits.go
@@ -36,11 +36,16 @@ func (h *Handlers) HandleTrackHabitActivity(ctx context.Context, request mcp.Cal
 		return reportMCPError("Missing or invalid required argument: habit_id")
 	}
 
-	performedOn, ok := request.Params.Arguments["performed_on"].(string)
-	if !ok || performedOn == "" {
+	performedOnStr, ok := request.Params.Arguments["performed_on"].(string)
+	if !ok || performedOnStr == "" {
 		return reportMCPError("Missing or invalid required argument: performed_on")
 	}
 
+	performedOn, err := lunatask.ParseDate(performedOnStr)
+	if err != nil {
+		return reportMCPError(fmt.Sprintf("Invalid format for performed_on: '%s'. Must be YYYY-MM-DD.", performedOnStr))
+	}
+
 	client := lunatask.NewClient(h.config.AccessToken)
 	habitRequest := &lunatask.TrackHabitActivityRequest{
 		PerformedOn: performedOn,