robfig/cron · error

too many slashes

Error message

too many slashes: %s

What it means

getRange splits an expression on '/' to separate the range from the step. An expression containing more than one '/' cannot be interpreted as range/step and is rejected with this error naming the expression.

Solutions

1. Use at most one '/' per field component (range/step)
2. Remove the duplicated step: "*/15" not "*/15/2"
3. Validate fields against a pattern like ^\S+/\S+$ allowing only one slash before parsing

Example fix

// before
sched, err := p.Parse("0 */2/3 * * *")
// after
sched, err := p.Parse("0 */2 * * *")

if strings.Count(field, "/") > 1 {
	return fmt.Errorf("field %q may contain at most one '/' step separator", field)
}

sched, err := parser.Parse(spec)
if err != nil {
	return fmt.Errorf("malformed step in cron spec %q: %w", spec, err)
}

When it happens

Trigger: Specs like "*/2/3" or "1-5/2/2" in any field; accidentally doubling the step syntax or pasting a URL/path fragment into a cron field.

Common situations: Typo with repeated step separators; generated specs where a step value itself contained a slash; copy-paste of strings like "*/15" from another context plus its own step.

Understand the failure class

Background: "Invalid ... format", "must be in format X", "does not look like a ..." — invalid argument format errors across CLI tools and libraries — this error's family across 17 libraries.

Related errors

• too many hyphens
• step of range should be a positive number
• multiple optionals may not be configured
• parser does not accept descriptors
• expected exactly fields, found

AI-assisted analysis of robfig/cron@bc59245fe1 (2026-09-07). Data as JSON: /api/errors/673ef6a8b7ca6aca. Report an issue: GitHub.

Appendix: source

Thrown at parser.go:301

	switch len(rangeAndStep) {
	case 1:
		step = 1
	case 2:
		step, err = mustParseInt(rangeAndStep[1])
		if err != nil {
			return 0, err
		}

		// Special handling: "N/step" means "N-max/step".
		if singleDigit {
			end = r.max
		}
		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
}

View on GitHub (pinned to bc59245fe1)