Name: SEO Foundations
Author: Markdowners

Search engines and users need the same thing: content that is real, unique, and easy to parse. Optimize for clarity first; the ranking follows.

Crawlability first

Every page that should be indexed must be reachable via a plain <a href> link from somewhere else on the site — content behind a JS-only click handler or a form submit may never be crawled.
Never block pages you want indexed via robots.txt; a stray Disallow: / left over from staging is one of the most common real-world SEO outages.
Return real HTTP status codes: a "not found" page must return 404 (or 410 for permanently gone), never 200 with "Page not found" text — a 200 tells search engines the page is valid content worth indexing.

Metadata is not optional

Every page needs a unique <title> (50–60 characters is the safe display width) and a unique meta description (~150–160 characters) — duplicate titles across pages actively hurt ranking, they don't just look sloppy.
Use exactly one <h1> per page, matching the page's actual topic, with a logical heading hierarchy below it (h2 → h3, no skipped levels used purely for styling).

URLs should be stable, human-readable, and lowercase with hyphens (/blog/how-payments-work, not /blog?id=4821). Never change a published URL without a 301 redirect from the old one.
Set a canonical URL on every page, especially ones reachable via multiple query-string variants (sorting, filtering, session params) — without it, search engines may index near-duplicate URLs separately and split ranking signal between them.

Thin or auto-generated pages with no unique value get filtered out of the index over time — every indexable page needs genuinely unique, useful content, not just a unique URL.
Never cloak content: what the crawler fetches (server-rendered HTML) must match what a user sees. Client-only rendering that hides real content behind a loading spinner risks the crawler seeing an empty shell.

Add structured data (JSON-LD) matching the page's actual content type (Article, Product, FAQPage, etc.) — it must accurately describe what's on the page; fabricated or mismatched structured data risks manual penalties.
Validate structured data before shipping; malformed JSON-LD is silently ignored, not "partially applied."

Treat Core Web Vitals (loading, interactivity, visual stability) as a ranking input, not just a UX nice-to-have — a slow, layout-shifting page is worse for both users and search visibility.
Design mobile-first; the mobile version of a page is what gets indexed and ranked by default.

Maintain an XML sitemap listing only canonical, indexable, 200-status URLs — including redirected, noindexed, or 404 URLs in a sitemap wastes crawl budget and signals a poorly maintained site.