nats-io/nats-server · error

expected boolean value, but got '%s'

Error message

expected boolean value, but got '%s'

What it means

An item classified as boolean was compared (case-insensitively via strings.ToLower) against the accepted sets true/yes/on and false/no/off, and matched none. The parser only accepts these literal spellings for booleans.

Source

Thrown at conf/parse.go:366

		}
	case itemFloat:
		num, err := strconv.ParseFloat(it.val, 64)
		if err != nil {
			if e, ok := err.(*strconv.NumError); ok &&
				e.Err == strconv.ErrRange {
				return fmt.Errorf("float '%s' is out of the range", it.val)
			}
			return fmt.Errorf("expected float, but got '%s'", it.val)
		}
		setValue(it, num)
	case itemBool:
		switch strings.ToLower(it.val) {
		case "true", "yes", "on":
			setValue(it, true)
		case "false", "no", "off":
			setValue(it, false)
		default:
			return fmt.Errorf("expected boolean value, but got '%s'", it.val)
		}

	case itemDatetime:
		dt, err := time.Parse("2006-01-02T15:04:05Z", it.val)
		if err != nil {
			return fmt.Errorf(
				"expected Zulu formatted DateTime, but got '%s'", it.val)
		}
		setValue(it, dt)
	case itemArrayStart:
		var array = make([]any, 0)
		p.pushContext(array)
	case itemArrayEnd:
		array := p.ctx
		p.popContext()
		setValue(it, array)
	case itemVariable:
		value, found, err := p.lookupVariable(it.val)

View on GitHub (pinned to 3a66a489d2)

Solutions

1. Change the value to one of: true, yes, on, false, no, off (case-insensitive).
2. Replace 1/0 with true/false.
3. Replace semantic words like enabled/disabled with yes/no.
4. Strip surrounding whitespace or quotes from the value in the config file.

Example fix

// before
feature_enabled = 1
// after
feature_enabled = true

var boolWords = map[string]bool{"true": true, "yes": true, "on": true, "false": true, "no": true, "off": true}
if !boolWords[strings.ToLower(raw)] {
	return fmt.Errorf("%q is not an accepted boolean", raw)
}

When it happens

Trigger: processItem (from parse) hits case itemBool with it.val such as 'TRUE ' with stray whitespace it doesn't trim differently, 'enabled', '1', '0', 't', 'ja', or an empty value.

Common situations: Users writing numeric booleans (1/0), YAML-style 'True' is fine but 'enabled'/'disabled' is not, localized words, or quotes/whitespace around the value.

Related errors

• float '%s' is out of the range
• expected float, but got '%s'
• expected Zulu formatted DateTime, but got '%s'
• variable reference for '%s' on line %d could not be parsed:
• error parsing include file '%s', %v

AI-assisted analysis of nats-io/nats-server@3a66a489d2 (2026-09-02). Data as JSON: /api/errors/76fc2f8caf9126dd. Report an issue: GitHub.