tljorgensen

Simple Post Inserter takes various inputs through the settings page and determines three things:
The content you wish to display in your posts, could be plain text, could be some HTML code. 
By default the admin of the site is responsible for any of the content submitted.
The location where the content should be displayed within the post.
Post restrictions. By default if no other setting but the content and location are declared, 
the plugin will insert the content in all of the posts available on the site. This may not be what you 
desire, but you can filter by post type, category, and ID.
Currently the only parameter for placement inside the posts is based off of total paragraphs in a post. 
This will likely change in a future update to something a little more sensible such as: lines of text or character counts.

Simple Post Inserter

Simple post inserter does what it sounds like. Insert some content into a post at your desired location.

YAHMAN

ZIPANG

When you enter the HTML code directly, the layout changes depending on the p and br tags that WordPress automatically inserts.
<pre><code>remove_filter( 'the_content', 'wpautop' );
</code></pre>
It can be solved by adding the above code. 
However, this will disable all auto-inserted p and br tags. 
It is not user-friendly.
This plugin can be partially disabled.
Just enter the part you want to disable in the shortcode.
<pre><code>[jo]your HTML code[/jo]
</code></pre>
The author of this plugin loves text editors.

Just Output

WordPress automatically inserts p and br tags, but disables them in shortcodes.

Simple Post Inserter vs Just Output