Search for advice on site structure and you get two camps. One says build silos: wall each topic off, link only inside the walls, and let relevance pool at the top. The other says build topic clusters: one overview page per topic, the supporting posts around it, all linked together. Both come with tidy diagrams. Neither diagram looks much like a real blog with six years of posts in it.
The good news is that you do not have to choose a religion. The two models share most of their good ideas. Where they differ, there is a clear answer, and the evidence for it is better than the evidence for the alternative. The rest of this guide is about building that answer on a WordPress site you already have.
Two models, defined properly
Strict silos
“Siloing” as an SEO term is most closely associated with Bruce Clay, whose agency has published guidance on it for many years. In its own definition, there are two ways to silo a site:
- Physical silos, built from the URL folder structure. Every page on a theme lives in that theme’s directory, like files in a filing cabinet:
/bathrooms/grout-repair/,/kitchens/worktops/. - Virtual silos, built from internal links alone. Pages on a theme link to each other and to the silo’s top landing page, whatever their URLs look like.
Bruce Clay recommends virtual silos, reinforced by physical ones where possible. The part that makes a silo strict is the linking rule: the same page says links between silos should be avoided, with an exception only for the top landing pages, and that no subpage in one silo should link to a subpage in another. The theory is that stray links between themes weaken each theme.
Topic clusters
The topic cluster model was popularised by HubSpot. Its research team published “Topic Clusters: The Next Evolution of SEO” in May 2017, describing experiments its staff had begun in 2016. In that model, one pillar page covers a broad topic, and the posts on related sub-topics link back to the pillar and to each other. HubSpot still teaches it in an updated version of the same guide.
Notice what is missing from that definition: any rule against linking to another cluster. The cluster is a grouping, not a wall.
The real difference: links between topics
Line the two models up and they agree on nearly everything. Group related content. Give each group a strong top page that summarises it. Link the members of a group to that top page and to each other. Put the top pages near the home page.
The disagreement is a single kind of link: a link from a post in one group to a post in another. Strict silos forbid it. Clusters allow it whenever a reader would follow it. Here is the same small home-improvement site drawn both ways.
Cross-topic links are not rare edge cases. On most real sites they are the links readers want most. A recipe blog’s post on proving dough in a cold kitchen belongs to the bread category, but the reader needs the post on oven temperatures, which lives under baking basics. A personal-finance blog’s post on paying off a car loan needs to mention the emergency-fund post in the savings category. A strict silo turns each of those into a detour through two landing pages, or more often into no link at all.
The grouping half of siloing is sound and worth keeping. It is the ban that does not hold up. There is no public evidence from Google, or from controlled tests anyone has published, that forbidding relevant links between topics improves rankings. There is plenty of reason to think it costs reader paths. Keep the grouping, drop the ban.
What Google has said about structure and folders
Google has never endorsed either model by name. What it has said is useful, and mostly about links and findability rather than folders.
- Folders help Google a little, on big sites. Google’s SEO starter guide says grouping similar topics in directories can help it learn how often URLs in each directory change, and frames that as mattering most on sites with more than a few thousand URLs. It also says not to rush into reorganising a site for this.
- URLs should be readable, not deep. The URL structure guidelines ask for logical, human-readable URLs with descriptive words. They set no depth limit and do not ask for topic folders.
- Slashes are not counted; clicks are. In a 2018 office-hours hangout, John Mueller said that Google does not count slashes in URLs, and that what matters a little is how easy content is to find, meaning how many clicks it takes from the home page. That is a point about how many clicks a page sits from home, not folders.
- A reasonable pyramid beats a flat list. In 2021 Mueller said he would aim for a pyramid structure over a super flat one, while warning that a structure made too deep is harder to crawl, as reported by Search Engine Journal. Clusters under a handful of pillars are exactly that kind of pyramid.
- Breadcrumbs describe the hierarchy. Google’s breadcrumb documentation describes them as showing a page’s position in the site hierarchy, and Google can use them in search results.
Read together, that is a fairly clear picture. A sensible hierarchy helps. Making pages easy to reach by links helps. The folder path is a minor signal and a usability nicety. And nothing Google has published supports banning relevant links between sections; its link guidance asks for links in context from related pages, without caring which section they are in.
Pros and cons, side by side
| Item | Strict silo | Topic cluster | Hybrid (recommended) |
|---|---|---|---|
| Grouping | Rigid: one silo per page, enforced by folders and links | Loose: a post belongs to a cluster by its links | One primary category per post, plus cluster links |
| Links between topics | Forbidden below the landing pages | Allowed where a reader would follow | Allowed, in context, sparingly |
| URLs | Usually folder-based (/topic/post/) | Anything; usually flat | Leave existing URLs alone |
| Best at | Very clean hierarchies: product catalogues, documentation | Blogs and content sites that grow by topic | Existing archives of any kind |
| Main cost | Cuts reader paths; posts that fit two topics are forced into one | Clusters blur without an owner; pillars go stale | Needs a little judgement on each cross-link |
| Risk of moving to it | High if it means changing post URLs | Low: it is all links | Low: links, menus and breadcrumbs only |
One thing the table does not show: both models fail the same way when nobody maintains them. A silo landing page or a pillar that has not been updated since 2023 does not link to anything published since, and those newer posts drift deeper into the archive every week. Whatever you choose, the habit of adding each new post to its group is what keeps the structure real.
Silos in WordPress: categories, folders and breadcrumbs
WordPress gives you two native grouping tools, categories and tags. Categories are the natural silo: hierarchical, usually one or two per post, with an archive page each.
Physical silos: the permalink question
To put the category in post URLs, you set a custom structure such as /%category%/%postname%/ under Settings → Permalinks. On a new site that is a legitimate choice. On an existing site it changes the URL of every post you have ever published, which is the single riskiest thing you can do to an archive for the sake of structure.
WordPress will sometimes rescue an old URL on its own: when a request 404s, it tries to guess the post from the slug and redirect to it. That is a fallback, not a migration plan. Every old URL needs a deliberate permanent 301 redirect, every internal link needs updating, and Google’s guide to moving URLs says a medium-sized site can take a few weeks or more to settle, with visibility fluctuating in the meantime. Given that Google does not count slashes, the upside is small. Our advice: do not change post permalinks on an established site to create silos.
Two more traps with category-based URLs. A post in two categories can only have one URL. WordPress core picks the category with the lowest ID, which is rarely the one you meant. SEO plugins let you choose a primary category instead, and Yoast’s own help page notes that changing the primary category changes the permalink when the category is in it. So recategorising a post later quietly moves it.
The category base
By default, category archives live at /category/kitchens/, and you can change that word under Settings → Permalinks → Category base. Both big SEO plugins offer to strip it altogether: in Yoast it is Yoast SEO → Settings → Categories → “Show the categories prefix in the slug”; in Rank Math it is Rank Math SEO → General Settings → Links → “Strip Category Base”. The vendors themselves are lukewarm. Yoast says the feature can cause unexpected URL behaviour and is not recommended in most cases; Rank Math’s documentation says it only affects aesthetics and that there is no evidence it helps SEO.
On an established site, leave it. Removing it changes every category archive URL and can collide with Pages that share a slug. If you removed it years ago, leave that alone too; flipping it back is a second migration.
Breadcrumbs
Breadcrumbs (Home › Kitchens › Worktops) are the cheapest structural win WordPress offers. They show readers and search engines where a post sits, link every post up to its category, and need no URL change at all. Core WordPress does not output them, but both main SEO plugins do:
- Yoast SEO: Yoast SEO → Settings → Advanced → Breadcrumbs, turn on “Enable breadcrumbs for your theme”, then place them with the Yoast Breadcrumbs block, the
[wpseo_breadcrumb]shortcode or a line of theme code, as Yoast’s breadcrumb guide describes. - Rank Math: Rank Math SEO → General Settings → Breadcrumbs (off by default). For the trail to follow your primary category, set Rank Math SEO → Titles & Meta → Posts → Primary Taxonomy to Categories, then pick the primary category in the post sidebar, as its primary category guide explains.
In Yoast, the primary category is the “Select the primary category” drop-down under Categories in the post sidebar. Set it for every post that has more than one category, so the breadcrumb tells the story you intend.
Clusters in WordPress: where the pillar page lives
A topic cluster in WordPress is a pillar page plus a set of posts, usually all in one category, joined by links you write. The only real decision is what the pillar is.
Stays out of the dated blog archive, feels permanent, and suits an evergreen overview such as “Bathroom renovation: the complete guide”. It has no category, so it is only reachable if you link it from the menu, a start-here page or the cluster posts.
Appears in feeds, archives and the category, carries a date, and can be your existing “complete guide” post. Good when the broadest post already exists, as it often does. Keep the date honest when you update it.
Free and automatic, but it is a date-ordered list that paginates. Add a written introduction (the category description, if your theme shows it) with links to the cornerstone posts. Useful as a backstop, weaker than a written pillar.
Whichever you choose, the pillar is a real piece of writing: a paragraph or two on each sub-question, with the link in the paragraph, not a bare list. Those are contextual links, and our guide to contextual and navigational links explains why they carry more than a menu or widget does. Then link the pillar from your menu, so every post in the cluster is two clicks from the home page.
The hybrid worth building
Here is the structure we recommend for almost every existing content site. It keeps the useful half of each model and needs no URL changes.
- A small number of categories, each one a cluster. Five to twelve for most blogs. Each post gets one primary category. Categories with three posts in them are not clusters; merge them.
- One written pillar per cluster, linked from the main menu or a start-here page, linking to every post in the cluster from a sentence.
- Every cluster post links up to its pillar near the top, and sideways to its closest neighbours.
- Cross-links between clusters, in context, when a reader would follow. The test: would the reader of this sentence plausibly want that page next? If yes, link it, whatever category it is in.
- Breadcrumbs from the primary category, so the hierarchy is visible without being baked into URLs.
- Existing URLs untouched. The structure lives in links, menus and breadcrumbs, which can all be changed and undone in an afternoon.
In Bruce Clay’s terms this is a virtual silo with the doors left open. In HubSpot’s, it is a topic cluster with a category attached. It also shows a search engine what you cover in depth, which is what people mean by topical authority, without pretending a reader only ever cares about one topic at a time.
Product catalogues and documentation have a genuine tree shape: a product belongs to one category, an article belongs to one product area. There, folder URLs and tight grouping suit the content, and if you are building from scratch they are a fine choice. Even there, cross-links (from a billing article to the account settings it mentions) are what readers need.
Restructuring an existing archive without breaking URLs
Moving an existing archive to the hybrid is mostly link work. Done in this order, it never changes a post URL, and anything you do change is redirected the same day.
- Take an inventory.
Export every published post with its URL, categories, word count, internal links in and out, and clicks from Search Console for the last 12 months. A crawl gives you links and depth; Search Console gives you which posts matter.
- Draw the clusters on paper first.
Group posts by what they answer, not by the categories you happen to have. Most archives of a few hundred posts land on five to twelve clusters, plus a pile of dated or off-topic posts that belong to none.
- Tidy categories, redirecting any archive you retire.
Merging two thin categories changes only the category archive URL if your post permalinks are /%postname%/ (check). Add a 301 from the old archive to the new one and update any menu or in-content links to it.
- Set one primary category per post.
In your SEO plugin, so breadcrumbs and any category-based URLs are consistent. If your permalinks include %category%, changing the primary category changes the URL, so skip this step for those posts or redirect them.
- Write or upgrade one pillar per cluster.
Start with the cluster that earns the most. Upgrade the existing broadest post where there is one, rather than publishing a new page that competes with it.
- Link the cluster: up, sideways, then across.
Each post to its pillar near the top; each to two or three neighbours; then cross-cluster links where a reader would follow. Use sentences you already wrote.
- Put pillars in the menu and switch on breadcrumbs.
This is the step that pulls whole clusters to two clicks from home.
- Recrawl and compare.
Check for broken links and links through redirects, compare click depth before and after, and leave Search Console numbers alone for at least a month before judging.
A reasonable pace is one cluster a week. That way each change is small enough to check, and if something goes wrong you know which week caused it. Before you start, run a crawl with the click depth checker so you have a baseline to compare against.
| Change | URLs affected | What to do |
|---|---|---|
| Add pillars, menus, breadcrumbs, links | None | Just do it |
| Merge or rename a category | That category’s archive pages | 301 the old archive; update links to it |
| Remove or change the category base | Every category archive | Avoid on an established site |
| Switch posts to /%category%/%postname%/ | Every post | Avoid; if unavoidable, 301 every URL and update every link |
| Change a post’s category with %category% in URLs | That post | 301 the old URL; update internal links |
While you are grouping, you will find pairs of posts answering the same question in different categories. Do not split links between them; pick one, as described in our guide to keyword cannibalization in WordPress (also spelled cannibalisation).
Three worked examples
A home-improvement blog with physical silos already
A 900-post DIY site has used /%category%/%postname%/ since launch: /bathrooms/…, /kitchens/…, /garden/…. The URLs are fine and stay exactly as they are. What changes is the linking. Each category gets a written pillar in the menu, and the in-content links open up: the grout repair post links to the kitchen splashback post, the decking stain post links to the fence paint post in another category. The silo becomes a cluster without a single redirect.
A SaaS help centre
A 250-article help centre is a genuine tree: billing, integrations, account settings, troubleshooting. Folder URLs suit it, and each section’s index page is its pillar. The mistake to avoid is enforcing the tree on links. An article on failed card payments must link to the one on updating billing contacts (same section) and to the one on email notifications not arriving (troubleshooting). The support tickets that a strict silo would generate are the evidence.
A travel site organised by destination
A 600-post travel site has categories by country. Its most useful content, though, runs across them: rail passes, packing, travelling with children. The fix is not a second category tree. It is a few cross-cutting pillars (“Rail travel in Asia”) linked from the menu, which link into posts across several country categories, plus direct links where a Kyoto itinerary mentions the Tokyo rail pass. Countries stay the primary category and the breadcrumb; themes become pillars.
In all three, the structure that does the work is the one readers can click. Judge your site architecture in clicks from the home page rather than folders in the address bar. The internal linking strategy guide covers the weekly routine that keeps clusters linked once they exist, and the internal link audit checklist is the quarterly check that they still are.
Where Silotree fits
The slow part of the hybrid is the sideways and cross-cluster links: reading old posts to find a sentence that already mentions the neighbour. Silotree suggests those links, each from a sentence you already wrote in a related post, and you approve or skip each one. It never writes inside headings, captions or buttons, saves a WordPress revision first, and can undo any batch. It also finds posts competing for the same Search Console queries, so you can pick a winner before you build a cluster around it. The free internal link checker shows orphans, broken links and click depth with no account, which is the baseline the migration above starts from. If you already rely on your SEO plugin’s link suggestions, our comparison of Silotree and Rank Math sets out what each does.
- Siloing: how to structure your website — Bruce Clay, Inc. Physical vs virtual silos; the rule against cross-silo links.
- Topic Clusters: The Next Evolution of SEO (May 2017, archived) — HubSpot Research
- Topic clusters (current version) — HubSpot
- SEO starter guide — Google Search Central
- URL structure best practices — Google Search Central
- Link best practices — Google Search Central
- Breadcrumb structured data — Google Search Central
- Site moves with URL changes — Google Search Central
- Google: click depth matters more than URL structure (2018 hangout) — Search Engine Journal
- Mueller on pyramid vs flat site structure (2021) — Search Engine Journal
- Settings → Permalinks screen — WordPress.org documentation
Questions people ask
Is a topic cluster just a silo with a different name?
Close, but not quite. Both group related pages under a strong top page. A strict silo forbids links from a post in one group to a post in another; a topic cluster allows them wherever a reader would follow. That single rule changes how readers move around the site.
Do I need my category in the URL to have a silo?
No. Bruce Clay, who popularised the term, describes virtual silos built purely from links as well as physical ones built from URL folders. Google has said it does not count slashes in a URL, so the grouping your links create matters far more than the folder path.
Should I remove /category/ from my WordPress URLs?
On an established site, usually not. It changes the address of every category archive, can clash with page slugs, and gains nothing measurable. If you have already removed it, leave it removed rather than switching back.
Should a pillar page be a WordPress Page or a post?
Either works. A Page stays out of the date-ordered blog archive and feels permanent; a post appears in feeds and archives and carries a date. What matters more is that the pillar is linked from your menu or a start-here page and is kept up to date as you publish.
Will cross-linking between topics dilute my relevance?
There is no public evidence that it does, and Google’s own guidance asks for links between related pages in context. A link from a bathroom tiling post to a kitchen splashback post is related in exactly the way a reader cares about. Unrelated links are the problem, whichever group they sit in.
How many posts should a topic cluster have?
Enough that the pillar has something real to summarise: usually five or more. Below that, a well-linked post on its own is fine. Very large clusters of fifty or more often split naturally into two pillars with a link between them.