Generate og:description from page content when not explicitly set #205

Copilot · 2025-10-27T20:45:02Z

Pages without explicit description in front matter currently fall back to the site-wide default, which may not be relevant. This PR generates descriptions by extracting and formatting text from page content.

Changes

New Liquid filter (lib/jekyll-theme-cs50.rb)

describe: Converts Markdown to HTML, extracts plain text, normalizes whitespace, truncates to ~160 chars at word boundaries
Excludes page title (first h1 tag) and table of contents (ul#markdown-toc) from the generated description

Updated layout (_layouts/page.html)

Three-tier priority: explicit page.description → generated from page.content → site.cs50.description

Example

Before:

<meta property="og:description" content="{{ page.description | default: site.cs50.description }}">

After:

{%- capture description -%}
    {%- if page.description -%}
        {{- page.description -}}
    {%- elsif page.content -%}
        {{- page.content | describe -}}
    {%- else -%}
        {{- site.cs50.description -}}
    {%- endif -%}
{%- endcapture -%}
<meta property="og:description" content="{{ description | strip }}">

Page with content but no explicit description now generates:

<meta property="og:description" content="This is an introduction with lots of interesting content that will be automatically extracted and used as the...">

Note: The generated description excludes the page title and table of contents, ensuring only the actual content is used.

Security: Passes CodeQL with 0 alerts.

Fixes Dynamically generate og:description from page contents #204

Original prompt

This section details on the original issue you should resolve

<issue_title>Dynamically generate og:description from page contents</issue_title>
<issue_description></issue_description>

Comments on the Issue (you are @copilot in this section)

Fixes Dynamically generate og:description from page contents #204

💡 You can make Copilot smarter by setting up custom instructions, customizing its development environment and configuring Model Context Protocol (MCP) servers. Learn more Copilot coding agent tips in the docs.

Co-authored-by: dmalan <788678+dmalan@users.noreply.github.com>

dmalan · 2025-10-28T13:57:25Z

_layouts/page.html

        {%- endif -%}

-        <meta property="og:description" content="{{ page.description | default: site.cs50.description }}">
+        {%- capture dynamic_description -%}


Change dynamic_description to description.

dmalan · 2025-10-28T13:57:42Z

_layouts/page.html

+            {%- if page.description -%}
+                {{- page.description -}}
+            {%- elsif page.content -%}
+                {{- page.content | generate_description -}}


Change generate_description to describe.

dmalan · 2025-10-28T13:58:24Z

lib/jekyll-theme-cs50.rb

+    def generate_description(input, max_length = 160)
+      return "" if input.nil? || input.to_s.strip.empty?
+
+      # Convert markdown to HTML first if possible


Change "markdown" to "Markdown"

dmalan · 2025-10-28T13:59:45Z

lib/jekyll-theme-cs50.rb

+          html = input.to_s
+        end
+      rescue StandardError => e
+        Jekyll.logger.debug "CS50: Could not convert markdown to HTML: #{e.message}"


dmalan · 2025-10-28T14:00:20Z

lib/jekyll-theme-cs50.rb

+      end
+
+      # Clean up whitespace
+      text = text.gsub(/\s+/, ' ').strip


Use double quotes.

dmalan · 2025-10-28T14:00:35Z

lib/jekyll-theme-cs50.rb

+      # Truncate to max_length, breaking at word boundary
+      if text.length > max_length
+        text = text[0...(max_length - 3)]
+        last_space = text.rindex(' ')


Use double quotes.

dmalan · 2025-10-28T14:00:42Z

lib/jekyll-theme-cs50.rb

+        text = text[0...(max_length - 3)]
+        last_space = text.rindex(' ')
+        text = text[0...last_space] if last_space && last_space > 0
+        text += '...'


Double quotes.

dmalan · 2025-10-28T14:02:52Z

lib/jekyll-theme-cs50.rb

+      # Convert markdown to HTML first if possible
+      begin
+        if defined?($site) && $site
+          html = $site.find_converter_instance(::Jekyll::Converters::Markdown).convert(input.to_s)


Replace lines 108–117 with just line 110, since we know it'll exist.

dmalan · 2025-10-28T14:03:50Z

lib/jekyll-theme-cs50.rb

+
+      # Parse HTML and extract text
+      begin
+        doc = Nokogiri::HTML5.fragment(html)


Replace lines 119–133 with just line 121 since we know it'll be installed.

dmalan · 2025-10-28T14:04:52Z

@copilot Make my changes.

Co-authored-by: dmalan <788678+dmalan@users.noreply.github.com>

Copilot · 2025-10-28T14:08:06Z

@copilot Make my changes.

Done in 5dbbf2b. Changes made:

Renamed dynamic_description → description
Renamed generate_description → describe
Updated comments: "markdown" → "Markdown"
Changed single quotes to double quotes
Simplified code by removing unnecessary error handling

dmalan

@copilot

dmalan · 2025-10-28T14:20:48Z

.gitignore


 node_modules/
+
+test_site/


Remove this line and whitespace.

Done in 3875fd3. Removed the blank line and test_site/ entry.

dmalan · 2025-10-28T14:21:51Z

lib/jekyll-theme-cs50.rb

+      html = $site.find_converter_instance(::Jekyll::Converters::Markdown).convert(input.to_s)
+
+      # Parse HTML and extract text
+      doc = Nokogiri::HTML5.fragment(html)


After converting to HTML, remove the page's title, which is the first h1 tag, and remove any table of contents, which would be the first ul with an id of #markdown-toc.

Done in 3875fd3. The describe filter now removes the first h1 tag and first ul#markdown-toc before extracting text for the description.

Co-authored-by: dmalan <788678+dmalan@users.noreply.github.com>

Initial plan

1452ee5

Copilot AI assigned Copilot and dmalan Oct 27, 2025

Copilot started work on behalf of dmalan October 27, 2025 20:45 View session

Copilot AI and others added 5 commits October 27, 2025 20:51

Add dynamic og:description generation from page content

752a6b9

Co-authored-by: dmalan <788678+dmalan@users.noreply.github.com>

Improve error handling in generate_description filter

a6f7d47

Co-authored-by: dmalan <788678+dmalan@users.noreply.github.com>

Add specific exception handling and logging to generate_description

bc440fd

Co-authored-by: dmalan <788678+dmalan@users.noreply.github.com>

Fix security vulnerabilities in HTML stripping fallback

5493826

Co-authored-by: dmalan <788678+dmalan@users.noreply.github.com>

Use consistent Sanitize configuration with codebase

f7eca3c

Co-authored-by: dmalan <788678+dmalan@users.noreply.github.com>

Copilot AI changed the title ~~[WIP] Dynamically generate og:description from page contents~~ Generate og:description from page content when not explicitly set Oct 27, 2025

Copilot AI requested a review from dmalan October 27, 2025 21:04

Copilot finished work on behalf of dmalan October 27, 2025 21:04

dmalan requested changes Oct 28, 2025

View reviewed changes

Copilot started work on behalf of dmalan October 28, 2025 14:05 View session

Address PR feedback: rename filter, simplify code, use double quotes

5dbbf2b

Co-authored-by: dmalan <788678+dmalan@users.noreply.github.com>

Copilot AI requested a review from dmalan October 28, 2025 14:09

Copilot finished work on behalf of dmalan October 28, 2025 14:09

dmalan requested changes Oct 28, 2025

View reviewed changes

Copilot started work on behalf of dmalan October 28, 2025 14:22 View session

Remove test_site from gitignore and exclude title/TOC from description

3875fd3

Co-authored-by: dmalan <788678+dmalan@users.noreply.github.com>

Copilot AI requested a review from dmalan October 28, 2025 14:27

Copilot finished work on behalf of dmalan October 28, 2025 14:27

updated comments

06354a3

dmalan marked this pull request as ready for review October 28, 2025 14:34

dmalan merged commit cef4059 into develop Oct 28, 2025
1 check passed

dmalan deleted the copilot/add-og-description-generation branch October 28, 2025 14:34

dmalan mentioned this pull request Oct 28, 2025

Generate per-page og:descriptions #124

Closed

Generate og:description from page content when not explicitly set #205

Generate og:description from page content when not explicitly set #205

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Copilot AI commented Oct 27, 2025 •

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