kataras/iris · warning

parameter is not a valid weekday

Error message

parameter is not a valid weekday

What it means

ErrParamNotWeekday is fired when a path parameter evaluated by the 'weekday' macro is not one of Go's long day names (Sunday, Monday, ..., Saturday), which map to time.Weekday values. The value must match a day name exactly (case-sensitive).

Source

Thrown at macro/macros.go:473

		}

		return paramValue, true
	})

	simpleDateLayout = "2006/01/02"

	// Date type.
	Date = NewMacro("date", "", time.Time{}, false, true, func(paramValue string) (any, bool) {
		tt, err := time.Parse(simpleDateLayout, paramValue)
		if err != nil {
			return fmt.Errorf("%s: %w", paramValue, err), false
		}

		return tt, true
	})

	// ErrParamNotWeekday is fired when the parameter value is not a form of a time.Weekday.
	ErrParamNotWeekday = errors.New("parameter is not a valid weekday")
	longDayNames       = map[string]time.Weekday{
		"Sunday":    time.Sunday,
		"Monday":    time.Monday,
		"Tuesday":   time.Tuesday,
		"Wednesday": time.Wednesday,
		"Thursday":  time.Thursday,
		"Friday":    time.Friday,
		"Saturday":  time.Saturday,
		// lowercase.
		"sunday":    time.Sunday,
		"monday":    time.Monday,
		"tuesday":   time.Tuesday,
		"wednesday": time.Wednesday,
		"thursday":  time.Thursday,
		"friday":    time.Friday,
		"saturday":  time.Saturday,
	}

View on GitHub (pinned to 7bedaf55a0)

Solutions

1. Send the exact capitalized long day name, e.g. /schedule/Monday.
2. Handle normalization in a custom macro (e.g. title-case input before lookup).
3. Use {day:string} and parse/validate manually if you need flexible input formats.

Example fix

// before
// GET /schedule/monday -> error

// after
// GET /schedule/Monday
app.Get("/schedule/{day:weekday}", h)

const LONG_DAYS = ['Sunday','Monday','Tuesday','Wednesday','Thursday','Friday','Saturday'];
if (!LONG_DAYS.includes(day)) day = LONG_DAYS[new Date(`${day} 1 2020`).getDay()] ?? 'Monday';

const LONG_DAYS = ['Sunday','Monday','Tuesday','Wednesday','Thursday','Friday','Saturday'] as const;
function isWeekdayName(v: string): v is typeof LONG_DAYS[number] {
  return (LONG_DAYS as readonly string[]).includes(v);
}

When it happens

Trigger: Route like app.Get('/schedule/{day:weekday}', h) with requests such as '/schedule/monday' (lowercase), '/schedule/Mon', or '/schedule/1' — only exact long names pass.

Common situations: Clients send abbreviated day names or non-English day names; case-sensitivity surprises (monday vs Monday); dates passed instead of day names.

Related errors

• errors joined from param parser: strings.Join(p.errors, "\n"
• parameter is not alphabetical
• parameter is not a file
• empty form
• no trailing path parameter found

AI-assisted analysis of kataras/iris@7bedaf55a0 (2026-08-30). Data as JSON: /api/errors/094221006e8b783a. Report an issue: GitHub.