nektos/act · error

%sExpected a scalar got %v

Error message

%sExpected a scalar got %v

What it means

Type error from Node.checkScalar (schema.go:262): the schema definition has no Mapping/Sequence/OneOf, so it expects a scalar, but the YAML node is a mapping, sequence, alias, or document node. The actual kind is rendered via getStringKind (document/sequence/mapping/scalar/alias/unknown).

Source

Thrown at pkg/schema/schema.go:262

	}

	isExpr, err := s.checkExpression(node)
	if err != nil {
		return err
	}
	if isExpr {
		return nil
	}
	if def.Mapping != nil {
		return s.checkMapping(node, def)
	} else if def.Sequence != nil {
		return s.checkSequence(node, def)
	} else if def.OneOf != nil {
		return s.checkOneOf(def, node)
	}

	if node.Kind != yaml.ScalarNode {
		return fmt.Errorf("%sExpected a scalar got %v", formatLocation(node), getStringKind(node.Kind))
	}

	if def.String != nil {
		return s.checkString(node, def)
	} else if def.Number != nil {
		var num float64
		return node.Decode(&num)
	} else if def.Boolean != nil {
		var b bool
		return node.Decode(&b)
	} else if def.AllowedValues != nil {
		s := node.Value
		for _, v := range *def.AllowedValues {
			if s == v {
				return nil
			}
		}
		return fmt.Errorf("%sExpected one of %s got %s", formatLocation(node), strings.Join(*def.AllowedValues, ","), s)

View on GitHub (pinned to 4f41128141)

Solutions

1. Go to the reported Line/Column and flatten the value to a scalar (plain string/number/bool)
2. Fix indentation so the value sits on the same logical line or as a quoted scalar
3. Replace anchors/aliases in scalar positions with literal values

Example fix

# before:
runs-on:
  - ubuntu-latest
# after:
runs-on: ubuntu-latest

# Keep constrained fields scalar: value on one line, or a quoted multi-line scalar (| / >) where allowed

// YAML kind guard before validation:
func isScalar(n *yaml.Node) bool { return n.Kind == yaml.ScalarNode }

Fatal validation error; restructure the YAML node to a scalar at the reported line/column.

When it happens

Trigger: Providing a block where a scalar is required: putting a nested map under `name:`, a YAML list under `runs-on:`, or an anchor/alias node where a plain string is expected.

Common situations: Indentation mistakes that turn a value into a nested mapping; copy-pasting a multi-line snippet into a scalar field; using YAML anchors (&x/*x) in scalar positions.

Related errors

• %sExpected a sequence got %v
• %sExpected a mapping got %v
• expressions are not allowed here
• %sFailed to parse: %s
• %sExpected one of %s got %s

AI-assisted analysis of nektos/act@4f41128141 (2026-08-15). Data as JSON: /api/errors/19f8a60310b9c461. Report an issue: GitHub.