knadh/listmonk · error

error compiling alt plaintext message: %v

Error message

error compiling alt plaintext message: %v

What it means

Compilation of the campaign's alternative plain-text message body failed during campaign preparation.

Source

Thrown at models/campaigns.go:207

	msgTpl, err := template.New(ContentTpl).Funcs(f).Parse(body)
	if err != nil {
		return fmt.Errorf("error compiling message: %v", err)
	}

	out, err := baseTPL.AddParseTree(ContentTpl, msgTpl.Tree)
	if err != nil {
		return fmt.Errorf("error inserting child template: %v", err)
	}
	c.Tpl = out

	if hasTplExpr(c.AltBody.String) {
		b := c.AltBody.String
		for _, r := range regTplFuncs {
			b = r.regExp.ReplaceAllString(b, r.replace)
		}
		bTpl, err := template.New(ContentTpl).Funcs(f).Parse(b)
		if err != nil {
			return fmt.Errorf("error compiling alt plaintext message: %v", err)
		}
		c.AltBodyTpl = bTpl
	}

	// Compile any header values that contain template expressions.
	for _, set := range c.Headers {
		for _, val := range set {
			if hasTplExpr(val) {
				c.HeaderTpls = make([]map[string]*txttpl.Template, len(c.Headers))
				break
			}
		}
		if c.HeaderTpls != nil {
			break
		}
	}
	if c.HeaderTpls != nil {
		var txtFuncs map[string]any = f

View on GitHub (pinned to 670c01717d)

Solutions

1. Fix the syntax error reported in the wrapped parse error
2. Escape literal braces with {{"{{"}}"
3. Validate alt body functions against the registered func map
4. Clear or simplify the alt body to confirm the error source

Example fix

// before
alt = "Hello {{ if .Name }}"
// after
alt = "Hello {{ if .Name }}{{ .Name }}{{ end }}"

if hasTplExpr(c.AltBody.String) {
    if _, err := template.New("alt").Funcs(funcMap).Parse(c.AltBody.String); err != nil {
        return fmt.Errorf("invalid alt body template: %v", err)
    }
}

if err := c.CompileTemplate(); err != nil {
    if strings.Contains(err.Error(), "error compiling alt plaintext message") {
        // highlight the alt-body editor field with the parse error
    }
}

When it happens

Trigger: AltBody is non-empty and contains template expressions (hasTplExpr true) with invalid syntax or unknown functions, so template.New(ContentTpl).Funcs(f).Parse(b) fails.

Common situations: Unbalanced {{ }} in the plaintext alt body; function typo; braces copied from HTML body with syntax invalid in text/template context; users often forget the alt body is also templated.

Related errors

• error compiling subject: %v
• error compiling base template: %v
• error compiling message: %v
• error inserting child template: %v
• campaigns.fieldInvalidSubject

AI-assisted analysis of knadh/listmonk@670c01717d (2026-09-01). Data as JSON: /api/errors/de270ba088caa4cd. Report an issue: GitHub.