Google historically has accounted for the canonical in a set of TOC anchor links, seeing the anchor link pages as a part of the main URL and not separate pages. Around late 2023, based on data that began to present itself within Google’s search console, I started speculating about the cause of what I seeing. What if the previously unthinkable happened?
What if Google no longer attributed anchor link URLs to the canonical url? What could go wrong?
What is a canonical when it comes to TOC anchor links?
Fundamentally, content with a table of contents section, the canonical is the URL of the page and the table of content at the top of the content has links that when clicked will jump down to that chapter on the page. Each chapter has its own link and typically that means every header tag in the article is linked in the table of content at the top.
For years in order to avoid accidentally creating duplicate content on our sites, the canonical named and set in the header as where all the “juice” was attributed. Plainly speaking, it is the ability to tell a search engine which version of a page should be considered the authoritative or main version so the anchors weren’t seen as separate pages. And it is communicated to search engine via an HTML tag in the header of a page. It looks like this:
<link rel=“canonical” href=“https://www.example.com/preferred-page-url/” />
Search engines will then understand that https://www.example.com/preferred-page-url/ is the primary page. And they will combine the ranking power from all the anchor text URLs into the canonical URL.
What are Table of Content Links?
Content organized using table of contents format uses the main URL and appends on the end of it a ‘#’. The html is coded some that if a visitor wants to quickly “jump” to the portion of the page they are interested in, these links provide a short cut. Its considered by many to be a way to be more “helpful” to a visitor.
Here’ might be some examples of how these would appear.
https://www.americanwaymedia.com/#indexationhttps://developers.google.com/search/docs/crawling-indexing/canonicalization#canonical-how
What problem does not having a canonical attribution create?
Using the examples above – here are ways that a search engine absent canonical instruction might get confused on which URL to consolidate all the page signals.
https://www.americanwaymedia.com/https://www.americanwaymedia.com/#indexation
https://developers.google.com/search/docs/crawling-indexing/https://developers.google.com/search/docs/crawling-indexing/#canonicalization
To our eye and experience we would understand that despite the hashtag keyword at the end of the second example, they are the same page, but to a search engine without additional instructions, they would be interpreted as separate pages.
The canonical system is a method of de-duplication and essential when it comes to storing data. If we had 20 digital copies of something that are the same, 19 of them can be discarded. They were all identical anyway, nothing was lost and we retain space to store the information saved.
So without canonical instruction, all those URLs that lead back to the same page would be interpreted as duplicate content. Duplicate content is multiple URLs that lead to the same content on the same domain versus syndicated content which is same content on different domains, i.e. press releases.
Why is duplicate content bad for SEO?
We can see that duplicate content occurs when multiple URLs lead to substantially similar or identical content. Having all these copies of the same content potentially can confuse search engines, diluting the ranking signals and adversely affecting the site’s search engine optimization (SEO).
In short, a working canonical system to recognize the main canonical is essential to ensure that our content is indexed and scored so all our efforts to get content to a searcher who is looking for what we can offer.
What if the canonical and each jump link were no longer combined into a single set of data
IF that happened, you’d see them indexed in Google Search Console – (I should have also demonstrated each also had a position ranking)
Screenshot of four URLS with hashtags in their URLS and all gaining separate impressions and clicks.
What If Google Started Seeing TOC Anchors as Separate Pages?
Forget writer intent. Forget gaming. Consider only this: table of contents jump links exist in your page’s source code, and they’re visible to any crawler that looks. What if a ranking system—especially one tuned for “helpful content”—started treating those anchors as distinct surfaces rather than ignoring them as fragments? [1]
That simple shift creates a parallel to what might have happened at the topical level: a de‑duplication mechanism that sees too many “page‑like” surfaces from one source and starts treating them as redundant.
The Detectability Problem: Anchors in the Source
Every TOC anchor creates a fragment identifier in the source:
e.g. https://www.americanwaymedia.com/#indexation
- Visible to Googlebot in the HTML.
- Clickable in the browser, creating URLs like /guide#crawl-budget
- One canonical URL (/guide) with ten distinct anchor destinations.
- Each anchor as a quasi‑independent “page” with its own content block.
- The page no longer as one monolithic document, but as a container for ten topic‑specific fragments.
Nothing about the writer’s intent changes. The anchors exist for user navigation. But their mere presence and detectability in the source gives the system the option to model them as separate pages.
The HCU‑Era Signal: Fragments Bloom, Then Vanish—Canonical Takes A Dive
During Helpful Content Update waves, the pattern was stark: anchor‑fragment URLs appeared in GSC data with sharp impressions spikes, then disappeared entirely. The canonical URL wasn’t spared—it got suppressed too. [2]
Key observations:
- Impressions surge: Hashtag URLs tracked as separate “pages,” impressions balloon to implausibly high levels (not just vs. canonical, but fragment‑vs‑fragment cannibalization).
- CTR flatlines: No proportional click increase—users land on the same page regardless of fragment, diluting efficiency.
- Total wipeout: Fragments vanish from GSC. Canonical drops off SERPs. Visibility goes to zero across the board. [3]
Scale to a TOC‑heavy site (200+ articles, each with 5–10 anchors):
- Per‑page: 1 canonical + 10 fragments = 11 surfaces.
- Domain‑wide: 200 articles × 11 = 2,200+ detectable “pages.”
- HCU trigger: If even a fraction get flagged as “unhelpful” (thin fragments, topical overlap), each acts as a domain signal that weighs down everything. [4]
Not page‑specific penalties. Sitewide suppression: the aggregate detectability of fragment surfaces across hundreds of pages creates a critical mass of “unhelpful” signals, collapsing the entire domain.
Fragment Anchor URLs Behave Like Separate Pages (In Theory)
If anchors are modeled as surfaces, a TOC‑dense site becomes a fragmentation factory:
Site scale |
Detectable surfaces per page |
Domain total (200 articles) |
HCU‑like outcome |
|---|---|---|---|
Single article |
1 canonical + 10 anchors |
11 |
Fragments bloom → vanish → canonical dies |
TOC‑heavy site |
Same × 200 pages |
2,200+ |
Sitewide suppression (each fragment drags) |
The source code multiplies the risk: every TOC makes more markup visible, every article scales it domain‑wide. HCU didn’t compress to “one or two pages”—it nulled the whole stack when fragmentation signals hit critical mass.
- Separate index entries.
- Canonical violations.
- Any attempt to manipulate rankings.
De‑duplication Goes Nuclear: From Fragments to Their Domains
The response isn’t gentle consolidation. It’s:
- Fragment purge: Hashtags drop from GSC entirely.
- Canonical suppression: Parent URLs deprioritized or delisted.
- Domain contagion: With 200+ TOC pages, each “unhelpful” fragment contributes to a sitewide score that tanks everything—no escapes.
This matches observed HCU behavior: not selective ranking drops, but wholesale visibility evaporation for sites where detectable markup (anchors) amplified thin/overlapping signals across scale. [5]
Now scale that logic. If anchors can be modeled as fragment‑surfaces, a helpful‑content‑style system might respond by de‑duplicating:
-
At the page level: “This one URL is generating too many surfaces. Treat it as one, suppress fragment visibility.”
-
At the topical level: “This site has too many pages with overlapping topic signals. Collapse them into fewer representatives.”
The parallel becomes clear:
Source Visibility + Scale = HCU‑Style Domain Kill
The model: HCU systems detected TOC anchors as separate pages, we watched the cannibalization unfold (impressions up, CTR flat), then Helpful Content applied domain‑level de‑duplication by zeroing out the noise.
- 200 TOC articles = thousands of fragment signals in source code.
- Each unhelpful tag compounds sitewide via sheer volume.
- Result: Fragments erased, canonicals buried, domain suppressed holistically.
Intent irrelevant. Scale + detectability does the damage. A single‑article experiment shows the mechanic; a table of content‑heavy site shows the apocalypse.
If you’re using table of contents and those links are visible in the source code when Google bots crawl your content, the solution is a plugin that obscures those links.