Google Unpacks How It Indexes Main Content—and Why Soft 404s Can Derail Your SEO

In a revealing talk at the recent Google Search Central Deep Dive event in Asia, Google’s Gary Illyes shed light on how Google identifies the main content—or what he calls “centerpiece content”—on web pages, and why soft 404 errors are among the most critical issues that can sabotage your site’s visibility in search.

The session, summarized by SEO expert Kenichi Suzuki, offers practical insights that every SEO, developer, and content creator should know, especially in an era where search is evolving rapidly thanks to AI and deeper semantic understanding.

What Exactly Is Main Content?

The term main content (MC) isn’t new to those who’ve reviewed Google’s Search Quality Rater Guidelines. It refers to the core part of a webpage that fulfills the user's intent—whether that’s a blog post, a product description, a calculator, or user-generated reviews.

Google defines main content as:

“Any part of the page that directly helps the page achieve its purpose… including text, images, videos, tools, and even user comments. The MC also includes the title at the top of the page.”

Illyes reinforced that centerpiece content plays a central role in both ranking and retrieval. In other words, this is the part of the page that Google weighs most heavily when deciding how to serve your content in search results.

“Google’s systems heavily prioritize the ‘main content’ of a page… Words and phrases located in this area carry significantly more weight than those in headers, footers, or navigation sidebars,” Suzuki summarized.

Editorial Insight: If you’re hiding your most valuable keywords in a sidebar or footer, you may be leaving rankings on the table. Structure matters—and Google is watching.

Google Uses Positional Analysis to Locate Content

To identify main content, Google doesn’t just read your HTML. It renders the page, then performs positional analysis—essentially determining where content physically appears on screen.

Illyes explained that Google assigns an importance score to different parts of a page. So if a key phrase appears in a sidebar, it’s considered less significant than if it appears in the main body.

“Moving a term from a low-importance area to the main content area will directly increase its weight and potential to rank,” Suzuki noted.

Semantic HTML—using elements like <main>, <header>, <aside>, and <footer> appropriately—can help disambiguate which sections of your page are most meaningful. In technical SEO, this is known as disambiguation, and it's increasingly important in a world of complex AI-driven search.

Indexing Isn’t About HTML—It’s About Tokens

A key takeaway from Illyes’ presentation is that Google doesn’t store raw HTML in its index. Instead, it tokenizes content—breaking it down into machine-readable units that fuel its understanding of context, semantics, and intent.

This is the same foundational process used in large language models (LLMs), which are reshaping how search engines interpret both queries and content.

What does this mean for SEO? Exact-match keywords matter less than ever. Google is focusing on understanding topics holistically. That’s a green light to focus on writing for users—not algorithms.

Soft 404s: The Silent SEO Killer

Perhaps the most urgent part of Illyes' discussion was his take on soft 404s, which he classified as a critical error—not just a minor issue.

A soft 404 occurs when a page that should return a "404 Not Found" status instead returns a "200 OK" code. This often happens when missing pages are redirected to the homepage or an error page that doesn’t declare itself as such.

Illyes explained:

“A page that returns a 200 OK status code but displays an error message or has very thin/empty main content is considered a ‘soft 404.’ Google actively identifies and de-prioritizes these pages as they waste crawl budget and provide a poor user experience.”

A surprising anecdote? For years, Google’s own soft 404 documentation page was mistakenly flagged as a soft 404 by their systems—and as a result, was not indexed.

The takeaway: Trying to “save PageRank” by redirecting broken URLs to your homepage is a risky move. In most cases, it’s better to return a genuine 404 or, when applicable, redirect to an appropriate replacement page.

Takeaways for SEOs and Content Teams

Here’s what to remember as you fine-tune your content strategy:

🧠 Prioritize Your Main Content

• Put your most valuable, topic-relevant text in the center of the page.
• Avoid hiding keywords in navbars or footers.

🧱 Use Semantic HTML

• Help Google disambiguate your layout by using semantic HTML elements.
• <main>, <article>, <section>, and <aside> aren’t just for accessibility—they also aid indexing.

💡 Think Tokens, Not Keywords

• Google indexes tokenized content, not your raw HTML.
• Focus on writing comprehensive, helpful content—topic relevance now outweighs keyword stuffing.

🚫 Don’t Fake 404s

• Avoid redirecting deleted content to unrelated pages.
• A 404 isn’t a bad thing—it’s better than creating a soft 404, which could cost you crawl budget and rankings.

Google Is Getting Smarter—Are You?

As search evolves beyond strings into meaning and context, it’s becoming critical to structure, present, and signal your content in a way Google’s systems can understand. That means fewer tricks, more clarity, and a renewed focus on real content quality.

Illyes’ message is clear: Stop thinking in shortcuts. If you want to rank, you need to build sites that clearly and honestly communicate value—to users and to machines.