Humanizr/Humanizer · error · InvalidOperationException

Template '{path}' must define a scalar 'value'.

Error message

Template '{path}' must define a scalar 'value'.

What it means

Thrown by ParseNamedTemplate when a 'template' entry is a mapping but either lacks a 'value' key or its value is not a scalar. Templates require a scalar 'value' string (optionally with a 'name'). Surfaced as compiler diagnostic HSG003 (severity Error).

Source

Thrown at src/Humanizer.SourceGenerators/Common/LocalePhraseNormalization.cs:432

                null or "" or "before-form" or "before" => CountPlacement.BeforeForm,
                "after-form" or "after" => CountPlacement.AfterForm,
                "none" => CountPlacement.None,
                var value => throw new InvalidOperationException($"Phrase '{path}.countPlacement' uses unsupported count placement '{value}'.")
            };

        static NamedTemplatePhrase ParseNamedTemplate(SimpleYamlValue value, string path, params string[] allowedPlaceholders)
        {
            if (value is SimpleYamlScalar scalar)
            {
                return CreateNamedTemplatePhrase(null, scalar.Value, path, allowedPlaceholders);
            }

            var mapping = ExpectMapping(value, path);
            RejectUnknownKeys(mapping, path, ["name", "value"]);
            var name = GetOptionalLiteral(mapping, "name", $"{path}.name");
            if (!mapping.TryGetValue("value", out var templateValue) || templateValue is not SimpleYamlScalar templateScalar)
            {
                throw new InvalidOperationException($"Template '{path}' must define a scalar 'value'.");
            }

            return CreateNamedTemplatePhrase(name, templateScalar.Value, path, allowedPlaceholders);
        }

        static NamedTemplatePhrase CreateNamedTemplatePhrase(string? templateName, string template, string path, params string[] allowedPlaceholders)
        {
            var placeholders = ImmutableArray.CreateBuilder<string>();

            foreach (var placeholderName in GetPlaceholderNames(template))
            {
                if (int.TryParse(placeholderName, out _))
                {
                    throw new InvalidOperationException($"Template '{path}' cannot use numeric placeholder '{{{placeholderName}}}'.");
                }

                if (placeholderName.Length == 0 || !char.IsLetter(placeholderName[0]) || placeholderName.Any(static c => !char.IsLetterOrDigit(c) && c != '_'))
                {

View on GitHub (pinned to ffc2b77c0f)

Solutions

1. Add a scalar 'value' string to the template mapping (e.g. value: '{count} {unit}').
2. If no name is needed, write the template as a plain scalar (template: '{count} {unit}').
3. Rebuild to confirm the diagnostic clears.

Example fix

# before
template:
  name: age
# after
template:
  name: age
  value: '{count} {unit} ago'

# Any template that is a mapping must contain a scalar 'value'.
yq -o=json '.. | select(has("template")) | .template | select(tag == "!!map" and (has("value") | not))' src/Humanizer/Locales/<code>.yml

When it happens

Trigger: Authoring template: { name: ... } with no value; making the value a mapping/sequence; misspelling 'value' as 'Value' or 'text'.

Common situations: Authoring a named template and forgetting the value field; YAML indentation making value a child of the wrong key; copy-paste from a doc snippet that omitted value.

Related errors

• Template '{path}' cannot use numeric placeholder '{{placehol
• Template '{path}' uses unsupported placeholder '{{placeholde
• Template '{path}' can only use placeholders: {allowedPlaceho
• Phrase '{path}' must define a scalar string or an explicit '
• Phrase '{path}' can only use placeholders in explicit 'templ

AI-assisted analysis of Humanizr/Humanizer@ffc2b77c0f (2026-08-13). Data as JSON: /api/errors/f2b9b32afd3f4b99. Report an issue: GitHub.