nektos/act · error

The following format string references more arguments than w

Error message

The following format string references more arguments than were supplied: '%s'

What it means

Thrown by format() when a placeholder index parses fine but exceeds the number of supplied arguments (len(replaceValue) <= index). E.g. format('{1} {2}', 'a') references argument 2 that was never passed.

Source

Thrown at pkg/exprparser/functions.go:103

			}

		case bracketOpen: // found {
			switch character {
			case '{':
				output += "{"
				replacementIndex = ""
				state = passThrough

			case '}':
				index, err := strconv.ParseInt(replacementIndex, 10, 32)
				if err != nil {
					return "", fmt.Errorf("The following format string is invalid: '%s'", input)
				}

				replacementIndex = ""

				if len(replaceValue) <= int(index) {
					return "", fmt.Errorf("The following format string references more arguments than were supplied: '%s'", input)
				}

				output += impl.coerceToString(replaceValue[index]).String()

				state = passThrough

			default:
				replacementIndex += string(character)
			}

		case bracketClose: // found }
			switch character {
			case '}':
				output += "}"
				replacementIndex = ""
				state = passThrough

			default:

View on GitHub (pinned to 4f41128141)

Solutions

1. Make every {N} have a matching argument at position N (0-based).
2. Count placeholders versus arguments; add the missing arguments.
3. Run actionlint on the workflow — it statically checks format() arity.

Example fix

# before
${{ format('{0} {1}', 'a') }}
# after
${{ format('{0} {1}', 'a', 'b') }}

func formatArityOK(tpl string, nargs int) bool {
  re := regexp.MustCompile(`\{(\d+)\}`)
  for _, m := range re.FindAllStringSubmatch(tpl, -1) {
    i, _ := strconv.Atoi(m[1])
    if i >= nargs { return false }
  }
  return true
}

When it happens

Trigger: Placeholders numbered higher than the argument count; deleting an argument but leaving its placeholder; assuming 1-based indexing when it is 0-based (format('{1}', only) with one arg).

Common situations: Refactoring expressions and dropping arguments; copy-paste from docs with more placeholders than args; off-by-one confusion because GitHub's format() is 0-based.

Related errors

• The following format string is invalid: '%s'
• Unclosed brackets. The following format string is invalid: '
• Closing bracket without opening one. The following format st
• Cannot convert value to JSON. Cause: %v
• Cannot parse non-string type %v as JSON

AI-assisted analysis of nektos/act@4f41128141 (2026-08-15). Data as JSON: /api/errors/660f3ba0576fd145. Report an issue: GitHub.