WPF - ToolTip with multibinding

I dont't know wich VS version you are using but:

<TextBlock Text="{Binding Description, StringFormat="Description : {0}{}"}">

does not even compile for me.

Just remove the " and the empty brackets like that:

<TextBlock Text="{Binding Description, StringFormat=Description : {0}">

You could also write it like this if you want the ":

<TextBlock>    <TextBlock.Text>        <Binding Path="Description" StringFormat="Description : {0}" />    </TextBlock.Text>    <ToolTipService.ToolTip>        <TextBlock>                    <TextBlock.Text>                        <MultiBinding StringFormat="Description : {0}{1}">                            <Binding Path="FirstDescription" />                            <Binding Path="SecondDescription" />                        </MultiBinding>                    </TextBlock.Text>        </TextBlock>    </ToolTipService.ToolTip></TextBlock>

I have tried the following code and that worked perfectly:

<TextBlock Margin="20" Foreground="Black" FontSize="20" FontFamily="Century Gothic" Text="{Binding Name1}">        <TextBlock.ToolTip>            <TextBlock>                <TextBlock.Text>                    <MultiBinding StringFormat="MultiBinded Tooltip : {0}{1}">                        <Binding Path="Name1"/>                        <Binding Path="Name2"/>                    </MultiBinding>                </TextBlock.Text>            </TextBlock>        </TextBlock.ToolTip>    </TextBlock>

Just delete empty brackets. Next code work as expected:

<TextBlock Text="{Binding Description, StringFormat='Description : {0}'}">    <ToolTipService.ToolTip>        <TextBlock>                    <TextBlock.Text>                        <MultiBinding StringFormat="Description : {0}{1}">                            <Binding Path="FirstDescription" />                            <Binding Path="SecondDescription" />                        </MultiBinding>                    </TextBlock.Text>        </TextBlock>    </ToolTipService.ToolTip></TextBlock>

If the StringFormat starts with a left brace { the XAML parser require you to escape it using a pair of braces {}. Otherwise the parser gets confused because braces also are used in the syntax of markup extensions.

Details are found in the XAML documentation for {} Escape Sequence / Markup Extension.

Also, you can't use double quotes with inline binding but single quotes is available.