Open Graph / Twitter Card Meta Tags

Overview

Eigen auto-injects Open Graph (og:*) and Twitter Card (twitter:*) meta tags into every page's <head> during the build pipeline. This ensures shared links on social media (Twitter/X, Facebook, LinkedIn, Slack, Discord, etc.) display rich preview cards with title, description, and image.

No template changes are required. The feature is always-on.

How It Works

SEO values are resolved from a three-layer cascade:
- Auto-derived defaults (title = site.name, og:type = "website", canonical URL = base_url + page path)
- Site-level defaults from [site.seo] in site.toml
- Per-page overrides from [seo] in template frontmatter
The rendered HTML is scanned for existing OG/Twitter meta tags.
Only missing tags are generated and injected into <head>.

Configuration

Site-level defaults (`site.toml`)

[site]
name = "My Blog"
base_url = "https://blog.example.com"

[site.seo]
title = "My Blog"                          # optional, falls back to site.name
description = "A blog about interesting things"  # optional
image = "/assets/default-share.jpg"        # optional, site-relative or absolute URL
og_type = "website"                        # default: "website"
twitter_site = "@myblog"                   # optional, Twitter @handle
twitter_card = "summary_large_image"       # default: "summary_large_image"

All fields are optional. If [site.seo] is omitted entirely, sensible defaults are used.

Per-page frontmatter

---
seo:
  title: About Us
  description: Learn about our team and mission
  image: /assets/about-hero.jpg
  og_type: website
  twitter_card: summary_large_image
  canonical_url: https://example.com/about
---

All fields are optional. When absent, site-level defaults are used.

Dynamic pages with template expressions

For dynamic pages, SEO field values can reference collection item data using minijinja template expressions:

---
collection:
  source: blog_api
  path: /posts
item_as: post
seo:
  title: "{{ post.title }} | My Blog"
  description: "{{ post.excerpt }}"
  image: "{{ post.cover_image }}"
  og_type: article
---

Expressions are resolved per-item using the same template context used for the page template.

Generated Tags

For a fully configured page, these tags are generated:

<!-- Open Graph -->
<meta property="og:title" content="Page Title">
<meta property="og:description" content="Page description">
<meta property="og:image" content="https://example.com/assets/share.jpg">
<meta property="og:url" content="https://example.com/about.html">
<meta property="og:type" content="website">
<meta property="og:site_name" content="My Site">

<!-- Twitter Card -->
<meta name="twitter:card" content="summary_large_image">
<meta name="twitter:title" content="Page Title">
<meta name="twitter:description" content="Page description">
<meta name="twitter:image" content="https://example.com/assets/share.jpg">
<meta name="twitter:site" content="@mysite">

<!-- Canonical URL -->
<link rel="canonical" href="https://example.com/about.html">

Tags are omitted when their value is not available:

No description at any level: og:description and twitter:description omitted
No image at any level: og:image, twitter:image omitted, twitter:card forced to "summary"
No twitter_site configured: twitter:site omitted

Duplicate Detection

If a template already contains OG/Twitter meta tags or a canonical link, the build pipeline detects them and does not inject duplicates. This allows template authors to manually control specific tags when needed.

URL Resolution

Image paths starting with / are resolved to absolute URLs using site.base_url
Already-absolute URLs (http:// or https://) are used as-is
Canonical URLs are auto-generated from site.base_url + page_path
/index.html paths are normalized to / in canonical URLs

Pipeline Position

SEO injection runs after preload/prefetch hints and before HTML minification. It does not run during dev server rendering.

Module

src/build/seo.rs -- single file containing all resolution, detection, generation, and injection logic.