The 404 error is the most recognisable failure on the web. Everyone has clicked a link and landed on a page that says “not found”. What most people do not think about is how that page got there, how many of them their own website is quietly serving, and how much each one costs in lost visitors and wasted search engine attention. A 404 checker answers those questions by scanning a site, testing every link, and listing the ones that lead nowhere.
This article explains what a 404 checker does, how the 404 status fits alongside the other codes that matter, why 404s accumulate even on well-run sites, how they damage SEO and conversions, and how to build a fix routine that keeps the count near zero.
The status codes a 404 checker looks for
When a browser requests a page, the server replies with a three-digit status code before it sends any content. A 404 checker reads that code for every link it tests. The codes that matter most are:
- 200 OK — the page loaded normally.
- 301 Moved Permanently — the page has a new address and the browser is sent there. Not an error, but chains of 301s slow pages down and leak ranking value.
- 302 Found — a temporary redirect. Fine when genuinely temporary, a problem when used for permanent moves.
- 404 Not Found — the server cannot find anything at that address.
- 410 Gone — the page was deliberately removed and will not return.
- 500, 502, 503 — the server itself failed. The page may exist but cannot be delivered.
A basic 404 checker flags anything in the 4xx and 5xx ranges. A good one also flags soft 404s, which are pages that return 200 OK but display an error message. These are invisible to status-code-only tools and are among the most damaging problems in technical SEO, because search engines see a page that claims to be fine while showing nothing useful.
Where 404s come from
Nobody sets out to create broken links, yet every site accumulates them. The usual sources are:
Deleted content. An old product, an expired promotion, a retired staff member’s author page. The page goes, but the links pointing to it stay.
Renamed URLs. A category restructure, a change to permalink settings, a move from /blog/ to /articles/. If no redirect is set, every old address becomes a 404.
Migrations. Moving between platforms or hosts almost always changes some URLs. Media folders in particular tend to move, breaking every image link at once.
Typos. A single wrong character in a pasted URL creates a 404 that no one notices until a reader clicks it.
External changes. The sites you link to restructure, delete pages and shut down. Pew Research found that a quarter of all web pages that existed between 2013 and 2023 were gone by late 2023, and about 8 percent of pages only one year old had already disappeared.
Discontinued products. On ecommerce sites, sold-out or retired products are the largest single source of 404s, and their URLs keep receiving traffic from search engines and external links long after the product is gone.
What a 404 costs
The direct cost is the visitor who hits the error. Some go back and try another link. Many leave. On a commercial site, a 404 on a pricing page, a product page or a step in the checkout funnel is revenue lost at the moment of highest intent.
The indirect costs come from search engines and are less visible but often larger.
Wasted crawl budget. Search engines visit a limited number of URLs on your site per crawl. Every visit to a 404 is a visit not spent indexing a real page. On a large site, a high 404 count directly slows how fast new content gets discovered.
Lost link equity. Internal links pass ranking strength between pages. A link to a 404 passes nothing. If a strong page links to a dead URL, the value that link should have carried simply disappears.
Negative quality signals. Visitors bouncing off error pages, and a site that looks unmaintained, are both patterns search engines notice.
Lost external backlinks. When another site links to a URL of yours that now returns 404, the backlink still exists, but it points at nothing. Redirecting that URL recovers the value. Leaving it as a 404 throws it away.
How a 404 checker works
A 404 checker is a crawler. You give it a starting URL. It requests that page, extracts every link on it, and adds each link to a queue. It then requests each queued URL, records the status code, extracts any new links, and continues until it has visited every reachable page.
The better checkers improve on this basic loop in several ways. They read your XML sitemap first so they find pages that nothing links to. They collapse query-parameter variants so the same page is not tested fifty times. They let you exclude URL patterns such as tag archives and pagination that generate noise. They read page content to catch soft 404s. They test images, scripts, stylesheets and documents, not just anchor tags. And they stream results as they go, so you can start fixing while the crawl continues rather than waiting for a final report.
For each broken link, a useful report shows three things: the failed URL, the page where the link appears, and the anchor text of the link. That last detail matters more than it sounds. With it, you open the source page, search for the anchor text, and land on the exact link that needs fixing. Without it, you are searching the whole page for a URL that might be anywhere.
Reading a 404 report
A first scan on a site that has never been checked can produce a long list. Do not panic and do not start at the top. Sort and prioritise.
Internal 404s first. These are pages on your own domain and you can fix every one. Group them by path. If twenty of them share a prefix like /old-shop/, a single redirect rule fixes all twenty.
Soft 404s second. These usually point to a template problem, such as a product page showing “unavailable” with a 200 status, or an empty category page. Fix the template so it returns a real 404 or 410, or restore the content.
Server errors third. A 5xx that persists across scans is a bug worth escalating. One that appears once and vanishes was probably a transient host issue.
Redirect chains fourth. Update links that hop through multiple redirects to point directly at the final URL.
External 404s last. Replace with the moved resource if you can find it, link to an archived copy if you cannot, or remove the link.
Fixing 404s: the four options
There are only four ways to resolve a 404, and choosing correctly matters.
Update the link. If you know where the page went, point the link there directly. This is the cleanest fix because it avoids a redirect.
Add a 301 redirect. If many pages link to the old URL, or if external sites do, redirect the old address to the new one. This preserves value from every source, including ones you cannot edit. Do not redirect everything to the homepage; search engines treat blanket homepage redirects as soft 404s.
Return a 410. If the content is gone for good and there is no sensible replacement, a 410 tells search engines to drop the URL from their index faster than a 404 would.
Remove the link. If none of the above applies, unlink the text. Plain text is better than a dead link.
Preventing 404s in the first place
Fixing is necessary, but prevention is cheaper. Three habits reduce the rate at which 404s appear.
Redirect before you delete. Whenever a page is removed or renamed, set the redirect first. This should be part of your content deletion checklist, not an afterthought.
Scan before you publish. A single-page check on a new article takes seconds and catches typos and links to unpublished drafts before readers see them.
Scan on a schedule. External links rot without any action on your part. A monthly full-site scan for most sites, weekly for high-volume publishers, catches new problems while they are still few.
404 checking on WordPress, Shopify and in the browser
The same crawl works on any platform, but the fixing step is faster when the checker lives where you edit.
On WordPress, a plugin can bring the report into wp-admin and let you edit or unlink each broken link directly, with the exact post and anchor listed for every hit. On Shopify, a web-based checker can scan any store today, and a dedicated app that checks products, collections and pages from inside the admin is in development. In the browser, a Chrome extension can scan the page in your current tab, highlight the broken links in place and let you fix them from a side panel, which is ideal for quick checks on a page a customer complained about.
Choosing a 404 checker
The features that matter are sitemap-first crawling, soft 404 detection, asset checking, exclusion patterns, live results, source page and anchor text in every result, shareable reports, and scheduled monitoring with alerts. Speed and crawl depth matter far less than most marketing suggests.
Broken Link Checker covers all of these. The free tier scans 250 pages per crawl with no account and nothing to install, allows two scans a day, and detects 404s, faulty redirects, soft 404s and SSL problems. A free account raises the limit to 50 scans a month and unlocks image, script and document checking. Paid plans add daily or weekly scheduled re-scans with email alerts, AI-assisted link fixes and a Pro WordPress plugin, and the same account gives you access to a wider suite of SEO tools including rank tracking, an internal link optimizer, an SEO and AEO audit and an uptime monitor.
The bottom line
Every site has 404s. The question is whether you find them before your visitors and search engines do. A 404 checker turns an invisible, ongoing problem into a short, specific list you can work through in an afternoon, and a scheduled scan keeps that list short for good. It is one of the cheapest, fastest and most reliable improvements you can make to any website, and there is no good reason to leave it undone.
