What causes "step of range should be a positive number: %s" in nats-io/nats-server?

Set the step to a positive integer, e.g. "*/5" or "1-30/2"

step of range should be a positive number: %s

Error message

step of range should be a positive number: %s

What it means

getRange requires the '/' step of a cron range to be a positive integer; a step that parsed to 0 (or was explicitly '0') is rejected. Steps like '/0' produce this error rather than silently matching nothing.

Source

Thrown at server/cron.go:231

		}
		if step > 1 {
			extra = 0
		}
	default:
		return 0, fmt.Errorf("too many slashes: %s", expr)
	}

	if start < r.min {
		return 0, fmt.Errorf("beginning of range (%d) below minimum (%d): %s", start, r.min, expr)
	}
	if end > r.max {
		return 0, fmt.Errorf("end of range (%d) above maximum (%d): %s", end, r.max, expr)
	}
	if start > end {
		return 0, fmt.Errorf("beginning of range (%d) beyond end of range (%d): %s", start, end, expr)
	}
	if step == 0 {
		return 0, fmt.Errorf("step of range should be a positive number: %s", expr)
	}
	return getBits(start, end, step) | extra, nil
}

// parseIntOrName returns the (possibly-named) integer contained in expr.
func parseIntOrName(expr string, names map[string]uint) (uint, error) {
	if names != nil {
		if namedInt, ok := names[strings.ToLower(expr)]; ok {
			return namedInt, nil
		}
	}
	return mustParseInt(expr)
}

// mustParseInt parses the given expression as an int or returns an error.
func mustParseInt(expr string) (uint, error) {
	num, err := strconv.Atoi(expr)
	if err != nil {

View on GitHub (pinned to 3a66a489d2)

Solutions

Set the step to a positive integer, e.g. "*/5" or "1-30/2"
Validate any programmatically-supplied step is >= 1 before building the schedule string
Remove the '/step' suffix entirely if every unit should match

Example fix

// before
 expr := "*/0"
// after
 expr := "*/1"

Defensive patterns

Strategy: validation

Validate before calling

if step := parseStep(seg); step == 0 {
    return fmt.Errorf("step must be >= 1 in %q", seg)
}

Prevention

Guard programmatically-supplied steps with a >= 1 check
Prefer omitting the step when every unit should fire

When it happens

Trigger: A cron field with a zero step, e.g. "*/0" or "1-30/0", parsed via parseCron -> getField -> getRange.

Common situations: Computing the step from a variable/config value that defaulted to 0; typo writing '/o' or '/0' intending a real interval.

Related errors

AI-assisted analysis of nats-io/nats-server@3a66a489d2 (2026-09-02). Data as JSON: /api/errors/aae7e8d89f857a79. Report an issue: GitHub.