301s, 404s, and Site Migrations: Don't Let a Redesign Destroy Your SEO

The most common tragedy in a website redesign isn't the design getting worse — it's traffic dropping by half the day after launch. The cause is usually simple: all the old URLs were replaced, and nobody told Google or your visitors where the new home is. This article covers redirect concepts and implementation in one pass, so your redesign doesn't pay for itself with years of accumulated search rankings.

Two numbers to understand first: 301 and 404

A 301 redirect is a server status code that means "this URL has permanently moved to a new location." Browsers automatically take visitors to the new URL, and search engines gradually transfer the ranking signals the old URL accumulated. Google's long-standing official position: a correctly configured 301 passes the original page's equity — you don't need to worry about "redirects costing you points."

A 404 means "page not found." Occasional 404s don't hurt your site's overall rankings — Google has said explicitly that 404s are a normal part of the web. But if a page that had rankings and inbound links turns into a 404, everything that page accumulated genuinely resets to zero, and every site linking to it now sends visitors into a dead end.

Changing URLs is like moving house: you're free to move, but leave a forwarding address at the old one. Skip that, and the mail carrier (Google) returns all your letters.

The standard site migration process

Whether you're changing domains, changing platforms, or restructuring URLs, the process is the same, and the core is a redirect map:

1. Inventory every old URL: pull the list from three sources — Search Console's performance report, GA's top pages, and your sitemap. Pay special attention to pages with organic traffic and backlinks; these are the ones that must not break.
2. Build a one-to-one mapping: each old URL maps to the new URL with the closest content. When there's no matching page, redirect to the most relevant category page — not everything to the homepage. Redirecting hundreds of old URLs wholesale to the homepage can be treated by Google as a 404 (a "soft 404"), which means you did the work for nothing.
3. Use 301, not 302: a 302 means "temporarily moved" and doesn't fully transfer equity. Permanent moves always get a 301.
4. Avoid redirect chains: A→B→C relays dilute the effect and slow things down. The map should send A directly to the final C.
5. Verify after launch: spot-check that mapped URLs actually respond with 301 and land in the right place, then use Search Console's URL Inspection to confirm what Google sees. If you changed domains, use Search Console's Change of Address tool to notify Google.

Dead-link checks: the post-redesign routine

However complete the redirect map, something slips through: an internal article still linking to an old URL, a retired page hiding in the menu. After launch, crawl the whole site with a tool (Screaming Frog, or a free online broken-link checker), list every internal link returning 404, and fix or remove each one. Search Console's Page Indexing report also lists the 404s Google has found — a free and authoritative source of checks.

Our team has an iron rule internally: no link is allowed to 404. For unfinished pages, we'd rather hide the entry point than leave a dead link for a visitor to step on. This isn't just an SEO issue — it's a trust issue. A visitor who clicks three links and finds two broken won't blame Google; they'll blame your brand.

The 404 page itself deserves design

No matter how careful you are, someone will mistype a URL or follow a stale external link. A good 404 page should: explain "this page doesn't exist" in your brand's voice, offer a search box or links to popular pages, and keep the full site navigation. One technical note: the 404 page must actually respond with a 404 status code — not a "fake 404" that returns 200. The latter leads search engines to keep indexing a pile of pages that don't exist.

When to bring in help

If your site has a dozen pages, building the redirect map yourself is entirely doable. But e-commerce sites easily have thousands of product and category pages plus parameterized URLs — the map needs rule-based batch processing, and redirects need to be configured at the server level to be efficient. If you're evaluating a redesign, start with Is It Time to Redesign Your Website? Five Signals to confirm the timing. And if you want a team to plan a migration that doesn't hurt SEO, take a look at our brand website design and development services — redirect planning should be a standard line item on any redesign quote, not emergency first aid after things go wrong.