grafana/k6 · error

unable to apply threshold %s over metrics; reason: %s is an

Error message

unable to apply threshold %s over metrics; reason: %s is an invalid operator

What it means

Reached the default branch of the operator switch in Threshold.run: the parsed threshold expression carries an operator token that is not one of >, >=, <=, <, ==, ===, !=. The parser (parseThresholdExpression) should reject unknown operators earlier, so hitting this guard means a mismatch between the scanner's accepted operator set and this switch — effectively an internal invariant check.

Source

Thrown at metrics/thresholds.go:71

	switch t.parsed.Operator {
	case ">":
		passes = lhs > t.parsed.Value
	case ">=":
		passes = lhs >= t.parsed.Value
	case "<=":
		passes = lhs <= t.parsed.Value
	case "<":
		passes = lhs < t.parsed.Value
	case "==", "===":
		// Considering a sink always maps to float64 values,
		// strictly equal is equivalent to loosely equal
		passes = lhs == t.parsed.Value
	case "!=":
		passes = lhs != t.parsed.Value
	default:
		// The parseThresholdExpression function should ensure that no invalid
		// operator gets through, but let's protect our future selves anyhow.
		return false, fmt.Errorf("unable to apply threshold %s over metrics; "+
			"reason: %s is an invalid operator",
			t.Source,
			t.parsed.Operator,
		)
	}

	// Perform the actual threshold verification
	return passes, nil
}

func (t *Threshold) run(sinks map[string]float64) (bool, error) {
	passes, err := t.runNoTaint(sinks)
	t.LastFailed = !passes
	return passes, err
}

type thresholdConfig struct {
	Threshold        string             `json:"threshold"`

View on GitHub (pinned to 01ffac6f24)

Solutions

1. Verify the operator token lists (operatorTokens in thresholds_parser.go) exactly match the cases handled in Threshold.run
2. Fix the threshold expression to use a supported operator: >, >=, <=, <, ==, ===, !=
3. Report the inconsistency as a k6 bug if the expression was produced by the parser

When it happens

Trigger: Thrown at metrics/thresholds.go:71 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/08f9693c293e997d. Report an issue: GitHub.