diagnose-seo

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Structured diagnostic for technical SEO problems. Use when the user asks about crawl issues, indexation problems, why pages aren't being indexed, robots.txt questions, canonical errors, sitemap issues, rendering problems, or general technical SEO troubleshooting. For Core Web Vitals and page speed, see audit-speed.

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Sourcecalm-north/seojuice-skills

Added on2026-02-28

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Diagnose SEO

Structured diagnostic framework for crawl issues, canonicalization errors, indexation problems, and rendering failures.

Diagnostic Approach

Technical SEO problems fall into four categories. Diagnose in this order — each layer depends on the previous one working correctly:

Crawlability — Can search engines find and access the pages?
Indexability — Are the pages allowed to be indexed?
Renderability — Can search engines see the full content?
Signals — Are the right signals (titles, structured data, links) in place?

Layer 1: Crawlability

Check these in order:

robots.txt

Fetch
```
[domain]/robots.txt
```
and review the rules
Look for overly broad
```
Disallow
```
rules blocking important paths
Verify
```
Sitemap:
```
directive points to the correct sitemap URL
Check for different rules per user-agent (Googlebot vs others)

Common mistakes:

```
Disallow: /
```
blocking the entire site (often left from staging)
Blocking CSS/JS files that Googlebot needs for rendering
Blocking API or AJAX endpoints that load dynamic content
Staging robots.txt accidentally deployed to production

XML Sitemap

Fetch the sitemap URL(s) and check:
- Does it return 200? Is it valid XML?
- Does it list all important pages?
- Does it exclude pages that shouldn't be indexed (404s, redirects, noindex pages)?
- Are
```
<lastmod>
```
  dates accurate and recent?
- For large sites: is there a sitemap index?

Site Architecture

Pages should be reachable within 3 clicks from the homepage
Check for orphan pages (no internal links pointing to them)
Check for redirect chains (page A → B → C — should be A → C)
Check for redirect loops

Server Response

Do all important pages return HTTP 200?
Check for unexpected 301/302 redirects
Check for soft 404s (page returns 200 but shows "not found" content)
Verify HTTPS is enforced (HTTP should 301 to HTTPS)

Layer 2: Indexability

Meta Robots / X-Robots-Tag

Check for
```
<meta name="robots" content="noindex">
```
on pages that should be indexed
Check HTTP headers for
```
X-Robots-Tag: noindex
```
Common cause: CMS accidentally applying noindex to pagination, tag pages, or new pages

Canonical Tags

Every page should have a
```
<link rel="canonical">
```
pointing to itself (self-referencing canonical)
Check for canonical tags pointing to wrong pages (common in paginated content, filtered URLs)
Check for conflicting signals: canonical says page A, but noindex is set, or the page redirects

Canonical diagnosis checklist:

Does the canonical URL match the actual URL?
Is the canonical URL accessible (returns 200)?
Does the canonical URL have the same content?
Is there only one canonical tag on the page?

Duplicate Content

Check for the same content accessible at multiple URLs:
- With and without trailing slash (
```
/page
```
  vs
```
/page/
```
  )
- With and without
```
www
```
  (
```
example.com
```
  vs
```
www.example.com
```
  )
- HTTP vs HTTPS
- URL parameters creating duplicate pages (
```
?sort=price
```
  ,
```
?page=1
```
  )
Each duplicate set needs one canonical URL; all others should redirect or use canonical tags

Layer 3: Renderability

JavaScript Rendering

Does the page content appear in the raw HTML source? Or is it loaded via JavaScript?
If JS-rendered: does Googlebot see the full content? (Use URL Inspection tool in Search Console)
Check for content hidden behind click events, tabs, or accordions
Check for lazy-loaded content that only appears on scroll

Core Content Visibility

Is the main content in the initial HTML? Or loaded async after page load?
Are important elements (titles, headings, product details) in the DOM on first render?
Check for content that requires login or cookies to view

Layer 4: Signals

Title Tags

Every page has a unique
```
<title>
```
Title includes the primary keyword
Under 60 characters (to avoid truncation in SERPs)
Descriptive and click-worthy

Meta Descriptions

Every important page has a meta description
150-160 characters
Includes target keyword and a value proposition
Unique per page

Heading Structure

One H1 per page containing the primary keyword
Logical heading hierarchy (H1 → H2 → H3, no skips)
Headings describe section content (not decorative)

Structured Data

Check for JSON-LD structured data appropriate to the page type
Validate with Google's Rich Results Test
Common types: Article, Product, FAQ, HowTo, BreadcrumbList, Organization

Hreflang (multilingual sites)

Check for correct
```
hreflang
```
tags linking language variants
Verify reciprocal tags (page A points to B, B points back to A)
Check for
```
x-default
```
tag

Output Format

Technical SEO Diagnosis: [domain]

Summary

Critical issues: [count]
Warnings: [count]
Passed checks: [count]

Findings by Layer

For each issue found:

Layer	Issue	Severity	Affected Pages	Fix
Crawlability	robots.txt blocks /blog/	Critical	All blog pages	Remove `Disallow: /blog/` from robots.txt
Indexability	Missing canonical tags	Warning	15 pages	Add self-referencing canonicals
...	...	...	...	...

Priority Fix List

Ordered by impact:

[Critical fix] — affects [n] pages, blocks [crawling/indexing/ranking]
[Warning fix] — affects [n] pages, reduces [signal quality]
...

Pro Tip: Run the free SEO Audit for a quick technical check, the Broken Link Checker to find dead links, and the Robots.txt Generator to fix crawl directives. SEOJuice MCP users can run
/seojuice:site-health
for a full technical report and
/seojuice:page-audit [domain] [url]
to drill into specific pages.