nektos/act · error

Missing parameters for %s expected >= %v got %v

Error message

Missing parameters for %s expected >= %v got %v

What it means

Validation error from checkSingleExpression in pkg/schema/schema.go when a function call inside a ${{ }} expression has fewer arguments than the function's declared minimum arity (from the GetFunctions table, e.g. contains/endsWith/startsWith need exactly 2, format needs >=1).

Source

Thrown at pkg/schema/schema.go:145

		switch exprNode.Token().Kind {
		case actionlint.TokenKindInt:
		case actionlint.TokenKindFloat:
		case actionlint.TokenKindString:
			return nil
		default:
			return fmt.Errorf("expressions are not allowed here")
		}
	}

	funcs := s.GetFunctions()

	var err error
	actionlint.VisitExprNode(exprNode, func(node, _ actionlint.ExprNode, entering bool) {
		if funcCallNode, ok := node.(*actionlint.FuncCallNode); entering && ok {
			for _, v := range *funcs {
				if strings.EqualFold(funcCallNode.Callee, v.name) {
					if v.min > len(funcCallNode.Args) {
						err = errors.Join(err, fmt.Errorf("Missing parameters for %s expected >= %v got %v", funcCallNode.Callee, v.min, len(funcCallNode.Args)))
					}
					if v.max < len(funcCallNode.Args) {
						err = errors.Join(err, fmt.Errorf("Too many parameters for %s expected <= %v got %v", funcCallNode.Callee, v.max, len(funcCallNode.Args)))
					}
					return
				}
			}
			err = errors.Join(err, fmt.Errorf("Unknown Function Call %s", funcCallNode.Callee))
		}
		if varNode, ok := node.(*actionlint.VariableNode); entering && ok {
			for _, v := range s.Context {
				if strings.EqualFold(varNode.Name, v) {
					return
				}
			}
			err = errors.Join(err, fmt.Errorf("Unknown Variable Access %s", varNode.Name))
		}
	})

View on GitHub (pinned to 4f41128141)

Solutions

  1. Add the missing argument(s) — check the arity table in schema.go GetFunctions (contains/endsWith/startsWith: 2, format: >=1, join: 1-2)
  2. Validate the workflow with actionlint or `act` schema validation before committing
  3. Test the expression in a scratch workflow step to confirm it evaluates

Example fix

# before:
if: ${{ startsWith(github.ref) }}
# after:
if: ${{ startsWith(github.ref, 'refs/tags/') }}
Defensive patterns

Strategy: validation

Validate before calling

// Verify arity against act's table before shipping the workflow:
var arity = map[string][2]int{"contains": {2, 2}, "endsWith": {2, 2}, "format": {1, 255}, "join": {1, 2}, "startsWith": {2, 2}}
// ensure len(args) is within [min, max] for every call you write

Try / catch

Fail validation with the message included; no retry. Fix the expression and re-validate.

Prevention

When it happens

Trigger: Calling a known expression function with too few args: ${{ contains() }}, ${{ startsWith(github.ref) }}, ${{ join() }}. The check compares v.min > len(funcCallNode.Args) using actionlint's parsed AST.

Common situations: Typos or copy-paste mistakes in workflow expressions; writing expressions against GitHub docs but forgetting an argument; refactoring an expression and dropping a parameter.

Related errors

AI-assisted analysis of nektos/act@4f41128141 (2026-08-15). Data as JSON: /api/errors/d1a79dca0c85aa68. Report an issue: GitHub.