grafana/k6 · error

'%s' is not a valid duration value

Error message

'%s' is not a valid duration value

What it means

Raised by Duration.UnmarshalJSON when the JSON value for a duration-typed option is neither a quoted string parseable by ParseExtendedDuration nor a bare number (interpreted as milliseconds). It is the fallback error for unparseable duration input.

Source

Thrown at lib/types/types.go:86

// UnmarshalJSON converts JSON data to Duration
func (d *Duration) UnmarshalJSON(data []byte) error {
	if len(data) > 0 && data[0] == '"' {
		var str string
		if err := json.Unmarshal(data, &str); err != nil {
			return err
		}

		v, err := ParseExtendedDuration(str)
		if err != nil {
			return err
		}

		*d = Duration(v)
	} else if t, errp := strconv.ParseFloat(string(data), 64); errp == nil {
		*d = Duration(t * float64(time.Millisecond))
	} else {
		return fmt.Errorf("'%s' is not a valid duration value", string(data))
	}

	return nil
}

// MarshalJSON returns the JSON representation of d
func (d Duration) MarshalJSON() ([]byte, error) {
	return json.Marshal(d.String())
}

// NullDuration is a nullable Duration, in the same vein as the nullable types provided by
// package gopkg.in/guregu/null.v3.
type NullDuration struct {
	Duration
	Valid bool
}

// NewNullDuration is a simple helper constructor function

View on GitHub (pinned to 01ffac6f24)

Solutions

1. Provide durations as strings like "30s", "1m", "2d" or as numbers meaning milliseconds
2. Check for typos such as missing units or stray characters

When it happens

Trigger: Thrown at lib/types/types.go:86 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of grafana/k6@01ffac6f24 (2026-08-18). Data as JSON: /api/errors/03133ee0b288c832. Report an issue: GitHub.