Guides: fix the problems a pre-publish check finds

Each guide starts from a real problem, like a Search Console status you don't recognise or a link preview with no picture, and walks through what is happening, why, how to check it, how to fix it and how to confirm the fix worked.

Every guide says plainly which parts a free checker on this site can confirm for you and which parts you have to check yourself. Nothing here promises how Google, Facebook or any other service will treat your page: they make their own decisions, and no outside tool can see inside them.

A page is missing from Google

Why isn't my page showing up on Google? Rule out the blockers you can check on the page itself, and know which causes no tool can see.
Excluded by ‘noindex’ tag Find where the noindex comes from (tag, HTTP header, CMS setting), remove it and confirm it's gone.
Blocked by robots.txt Find the exact rule that blocks a URL, change it safely, and avoid mixing robots.txt with noindex.
Alternate page with proper canonical tag Google says there is nothing to do. How to spot the cases that aren't: a canonical to staging or to a URL that fails.
Sitemap could not be read / Couldn't fetch Check what the sitemap URL actually returns before you resubmit it.
Crawled / Discovered, currently not indexed Two Search Console statuses that look alike, what each one actually means, and which of them you can do something about.
Duplicate without user-selected canonical Google picked a main version because you didn't. How to make the choice yourself and stop generating the duplicates.
Soft 404 A page that says "not found" while answering 200. How to spot it in a minute, including the version we had on this site.
Page with redirect What the status means, when to leave it alone, and how to fix a Redirect error. Tried on real redirect chains.
Blocked due to access forbidden (403) Why Google gets a 403 your browser doesn't, how to verify Googlebot, and what our checker can and can't see.
Server error (5xx) What Google does with a 5xx, how long it waits, how to find the cause, and what a checker can and can't see.
Not found (404) Whether to fix a 404 in Search Console, when to redirect, and how to make sure a 404 page really answers 404.
Duplicate, Google chose different canonical than user You declared a canonical and Google disagreed. What Google weighs, how to see its choice, and what to fix.
Can I use noindex and a canonical tag together? What Google says, what we found no answer to, and how our checker treats the pair, with five test pages.
How to add a noindex meta tag The syntax, noindex vs nofollow vs none, the header version, and what our checker sees on twenty test pages.

A shared link looks wrong

Open Graph image not showing Work through tags, image URL, response, size, crawler access and cache to find which one fails.
What size should an og:image be? What Facebook, LinkedIn, X, WhatsApp, Slack and Google document, and how our checker rated eleven test images.

Something on the page is broken

Mixed content warnings Find every http:// file on an https page, and why browsers block some and try to upgrade others.
Unparsable structured data Find the JSON-LD block Google can't read (a trailing comma, a stray quote, an empty value) and fix it at its source.
Broken image icon on a website The causes from 404s to HTML served as an image, how to find each in DevTools, and what our checker misses.

Deciding who may crawl your site

Block AI crawlers in robots.txt The tokens for OpenAI, Anthropic, Google and others, what each controls, and what five real robots.txt files do.

Before you launch

Website launch checklist What to verify on each page before launch, how to verify it, and what only you can check.

Using fonts and images you didn't make

Can I use this font commercially? What a font file can and can't tell you about its license, tried on three real fonts.
How to credit a Creative Commons image Title, author, source and license, worked through on a real CC BY-SA 4.0 photo.
Can I combine CC BY and CC BY-SA? Collection or remix, what ShareAlike, NonCommercial and NoDerivatives require, and ten combinations tried on our checker.

Prefer to check straight away?

The Website Pre-Publish Checker runs every page-level check in one pass: indexing signals, title and description, link preview tags and image, broken links and files, image alt text, structured data and HTTPS. The robots.txt and sitemap checks are separate because they look at the whole site rather than one page.