grafana/k6 · error

' ' is an invalid value for metric ' ', a number or a…

Error message

'%s' is an invalid value for metric '%s', a number or a boolean value is expected

What it means

Produced by the raiseNan helper inside Metric.add when the value passed to Counter.add/Value.add etc. cannot be coerced to a number. After sobek coercion the value's float is NaN (e.g. null, a non-numeric string) while its boolean coercion is true; the invalid value (length-limited to 100 chars) and metric name are reported. Depending on the throw option this is either returned as an error or only logged as a warning while add() returns false.

Solutions

1. Pass a number or boolean to the metric's add() method, e.g. myCounter.add(1)
2. For boolean semantics use true (recorded as 1) rather than null or strings
3. Check state.Options.Throw: with throw disabled the error is only a warning and the sample is silently dropped

When it happens

Trigger: Thrown at internal/js/modules/k6/metrics/metrics.go:92 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/eaedacdb01251f60. Report an issue: GitHub.

Appendix: source

Thrown at internal/js/modules/k6/metrics/metrics.go:92

	}, string(omitMsg))
}

func (m Metric) add(v sobek.Value, addTags sobek.Value) (bool, error) {
	state := m.vu.State()
	if state == nil {
		return false, ErrMetricsAddInInitContext
	}

	// return/throw exception if throw enabled, otherwise just log
	raiseErr := func(err error) (bool, error) { //nolint:unparam // we want to just do `return raiseErr(...)`
		if state.Options.Throw.Bool {
			return false, err
		}
		state.Logger.Warn(err)
		return false, nil
	}
	raiseNan := func() (bool, error) {
		return raiseErr(fmt.Errorf("'%s' is an invalid value for metric '%s', a number or a boolean value is expected",
			limitValue(v.String()), m.metric.Name))
	}

	if v == nil {
		return raiseErr(fmt.Errorf("no value was provided for metric '%s', a number or a boolean value is expected",
			m.metric.Name))
	}
	if sobek.IsNull(v) {
		return raiseNan()
	}

	vfloat := v.ToFloat()
	if vfloat == 0 && v.ToBoolean() {
		vfloat = 1.0
	}

	if math.IsNaN(vfloat) {
		return raiseNan()

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