pcdr.marty

Automatically send HTTP Header “last-modified”. 
You can use post last modification time or creation date… (settings in administration)

Last modified header

Automatically send HTTP Header "last-modified".

djm56

Micro Site Care: Post Last Updated Date adds a last-updated date label to your posts and pages. It is lightweight, uses no JavaScript, and integrates cleanly with any theme.
Key features:
<ul>
<li>Show the last-updated date automatically before content, after content, or in both positions.</li>
<li>Set placement to Manual and use the template tag in your theme for full control over where the label appears.</li>
<li>Customise the label text with a flexible template — use <code>%s</code> to insert the date, or omit it to show a static label.</li>
<li>Choose between the WordPress site date format or a custom PHP date format string.</li>
<li>Optionally suppress the label when the modified date matches the publish date (suppress unchanged posts).</li>
<li>Target specific post types, or exclude selected post types from an all-types baseline.</li>
<li>Clean HTML5 <code><time></code> element output with an ISO 8601 <code>datetime</code> attribute for SEO and screen readers.</li>
<li>Developer-friendly: four filter hooks to customise visibility, label, CSS classes, and final HTML output.</li>
<li>Compatible with MSC Post Last Updated Date Pro for relative dates, style presets, per-post overrides, and shortcodes.</li>
</ul>

Micro Site Care: Post Last Updated Date

Display and control the last-updated date for your WordPress posts and pages, with flexible placement and label options.

Last modified header vs Micro Site Care: Post Last Updated Date