labstack/echo · error

unsupported value type: %T

Error message

unsupported value type: %T

What it means

Returned by bindValue (binder_generic.go:567-569) when the destination type matches none of the supported switch cases: bool, floats, ints, uints, string, time.Duration, time.Time, BindUnmarshaler, encoding.TextUnmarshaler, json.Unmarshaler. T fell through to the default branch.

Source

Thrown at binder_generic.go:568

			if err != nil {
				return err
			}
		}
		*d = t.In(to.ToInLocation)
	case BindUnmarshaler:
		if err := d.UnmarshalParam(value); err != nil {
			return err
		}
	case encoding.TextUnmarshaler:
		if err := d.UnmarshalText([]byte(value)); err != nil {
			return err
		}
	case json.Unmarshaler:
		if err := d.UnmarshalJSON([]byte(value)); err != nil {
			return err
		}
	default:
		return fmt.Errorf("unsupported value type: %T", dest)
	}
	return nil
}

View on GitHub (pinned to 05489dc173)

Solutions

1. Implement echo.BindUnmarshaler, encoding.TextUnmarshaler, or json.Unmarshaler on the type
2. Use c.Bind for whole structs rather than ParseValue per field
3. Use ParseValues[T] with a slice element type for repeated values

Example fix

// before
type Color struct{ R, G, B int }
v, err := echo.ParseValue[Color]("#fff")
// after — implement TextUnmarshaler:
func (c *Color) UnmarshalText(b []byte) error { /* parse hex */ return nil }
v, err := echo.ParseValue[Color]("#fff")

var z T
switch any(z).(type) {
case echo.BindUnmarshaler, encoding.TextUnmarshaler, json.Unmarshaler:
    // ok
default:
    // fall back to c.Bind for the whole struct
}

func isBindable[T any]() bool {
    var z T
    switch any(z).(type) {
    case echo.BindUnmarshaler, encoding.TextUnmarshaler, json.Unmarshaler:
        return true
    }
    return false
}

When it happens

Trigger: ParseValue[MyStruct](...) where MyStruct implements none of the unmarshaler interfaces; arrays/maps; pointers to unsupported types; structs without a custom unmarshaler.

Common situations: Binding a complex struct field from a single scalar value instead of using c.Bind; nested types; third-party types lacking TextUnmarshaler.

Related errors

• options are only supported for time.Time, got %T
• binding element must be a struct
• query/param/form tags are not allowed with anonymous struct
• unknown type
• binding to multipart.FileHeader struct is not supported, use

AI-assisted analysis of labstack/echo@05489dc173 (2026-08-04). Data as JSON: /data/errors/4f588aa019657ae2.json. Report an issue: GitHub.