SEO Metrics Reference — SEO Crawler

1. On-Page SEO

Core content and meta data elements that search engines use to understand and rank your pages.

Metric	Description	Why Important	Recommendation
Title Tag	The <title> element content	Primary ranking factor, shown in search results	30–60 characters, unique per page
Title Length	Character count of the title	Too long titles get truncated in SERPs	Keep between 30 and 60 characters
Meta Description	<meta name="description"> content	Shown as snippet in search results, affects CTR	70–160 characters, unique, compelling
Meta Robots	Directives like noindex, nofollow	Controls search engine crawling and indexing	Only use when intentionally blocking pages
Meta Viewport	<meta name="viewport"> tag	Required for mobile-first indexing	Include `width=device-width, initial-scale=1`
Canonical URL	<link rel="canonical"> href	Prevents duplicate content issues	Every page should have a self-referencing canonical
Word Count	Number of visible text words	Thin content ranks poorly	Minimum 200 words for indexable pages
Text-to-HTML Ratio	Ratio of visible text to total HTML	Very low ratio may indicate bloated code or thin content	Aim for >10%, ideally >25%
Content Hash	SHA-256 hash of page content	Detects exact duplicate pages	Each page should have unique content
html lang	<html lang="..."> attribute	Tells search engines the page language	Always set to the correct BCP-47 code
Content-Language	HTTP Content-Language header	Supplementary language signal	Should match html lang attribute
Meta Charset	Character encoding declaration	Ensures correct text rendering	Use UTF-8
Indexable	Whether the page can be indexed	Derived from meta robots, canonical, X-Robots-Tag	Important pages should be indexable

2. Headings

Heading tags (H1–H6) create the semantic structure of a page. A correct heading hierarchy is essential for SEO and accessibility.

Metric	Description	Why Important	Recommendation
H1 Tag	Primary heading of the page	Strongest on-page heading signal	Exactly one H1 per page
H2–H6 Tags	Subheadings at various depth levels	Structure content for users and search engines	Use logical nesting (H2 under H1, H3 under H2, etc.)
Heading Outline	Document-order sequence of all headings	Shows the actual reading structure of the page	Should form a consistent tree without skipped levels
Heading Hierarchy	Visual tree of heading nesting	Makes structural issues immediately visible	Available as interactive graph in the page profile

Heading Issues Detected

Issue	Severity	Description
`missing_h1`	Warning	Page has no H1 tag — every page needs a primary heading
`multiple_h1`	Warning	Page has more than one H1 tag — should have exactly one
`heading_hierarchy_skip`	Warning	Heading levels are skipped (e.g., H1 → H3 without H2). Indicates broken semantic structure
`heading_no_h1_first`	Warning	First heading on the page is not H1 (e.g., starts with H2 or H3)
`no_headings`	Warning	Page has content (>50 words) but no heading tags at all
H1 too long	Info	H1 text exceeds 70 characters — may get truncated
H1 very short	Info	H1 text is under 10 characters — may be too generic
Duplicate H1	Info	Multiple H1 tags with identical text

3. Links

Internal and external link analysis — the backbone of how search engines discover and evaluate pages.

Metric	Description	Why Important	Recommendation
Internal Links	Links pointing to pages on the same domain	Distribute PageRank and help discovery	Important pages should have many internal links
External Links	Links pointing to other domains	Provide context and authority signals	Link to relevant, authoritative sources
Internal Link Count	Number of outgoing internal links per page	Pages with few links pass less value	Include contextual internal links
External Link Count	Number of outgoing external links per page	Too many can dilute page authority	Keep reasonable, link only to quality sources
Inlinks	Number of incoming internal links to a page	Higher = more internal authority	Ensure important pages have many inlinks
Nofollow Links	Links with rel="nofollow/ugc/sponsored"	Tells search engines not to pass PageRank	Don't nofollow internal links
Broken Links	Links returning 4xx/5xx status codes	Bad user experience, wastes crawl budget	Fix or remove all broken links
Orphan Pages	Pages with no incoming internal links	Hard for search engines to discover	Link to every important page internally
Redirect Chains	Multiple redirects in sequence	Slow down crawling, lose PageRank	Maximum 1–2 redirects, prefer direct links
Link Depth	Click distance from start URL	Deep pages get crawled less frequently	Important pages within 3 clicks of homepage
Anchor Text	Clickable text of links	Gives context to linked page	Use descriptive, relevant anchor text
Found On URL	Parent page where link was discovered	Helps trace link origin	Useful for debugging link issues

4. Images

Image optimization affects both SEO and page performance.

Metric	Description	Why Important	Recommendation
Image Src	URL of the image file	Identifies the image resource	Use descriptive filenames
Alt Text	Alternative text attribute	Critical for accessibility and image SEO	Describe the image content naturally
Missing Alt	Image has no alt attribute	Accessibility violation, missed SEO opportunity	Every informative image needs alt text
Image Format	File format (JPEG, PNG, WebP, AVIF, SVG)	Modern formats offer better compression	Use WebP or AVIF for photos, SVG for icons
Lazy Loading	`loading="lazy"` attribute or data-src	Improves initial page load performance	Use lazy loading for below-the-fold images
Srcset	Responsive image srcset attribute	Serves appropriate image size per device	Provide multiple sizes for responsive images
Decorative	Empty alt attribute (`alt=""`)	Correctly marks non-informative images	Use `alt=""` for purely decorative images
Dimensions	Width and height attributes	Prevents layout shift (CLS)	Always specify width and height
File Size	Image file size in bytes	Large images slow page loading	Compress images, keep under 100KB

5. Technical SEO

Server-side and technical configuration that affects how search engines crawl and index your site.

Metric	Description	Why Important	Recommendation
HTTP Status Code	Server response status (200, 301, 404, etc.)	Determines page availability	Pages should return 200; fix 4xx/5xx errors
Redirects	301/302/307/308 redirections	Consolidate signals, guide users	Use 301 for permanent, minimize chains
robots.txt	Crawling directives file	Controls what search engines can access	Don't block important content
Sitemap.xml	List of URLs for search engines	Helps discovery of all pages	Include all indexable pages
HTTP Version	HTTP/1.1, HTTP/2, or HTTP/3	HTTP/2+ offers better performance	Use HTTP/2 or HTTP/3
Content-Encoding	Compression method (gzip, brotli)	Reduces transfer size 60–80%	Enable gzip or Brotli compression
Cache-Control	Caching directives header	Reduces server load, speeds up revisits	Set appropriate caching for static resources
ETag	Entity tag for cache validation	Enables efficient cache revalidation	Configure ETags on your server
Last-Modified	Last modification timestamp	Cache validation header	Set for all static resources
Meta Refresh	<meta http-equiv="refresh">	Client-side redirect, bad for SEO	Use server-side redirects instead
Pagination	rel="next"/rel="prev" links	Helps search engines understand paginated content	Implement on paginated series
Soft 404	200 status but "not found" content	Wastes crawl budget	Return proper 404 status codes
X-Robots-Tag	HTTP header indexing directives	Alternative to meta robots	Use for non-HTML resources
JS Dependency	Page relies on JavaScript for content	Search engines may not render JS	Ensure critical content is in initial HTML

6. Structured Data

Schema.org markup that enables rich results in search engines.

Metric	Description	Why Important	Recommendation
JSON-LD	JavaScript Object Notation for Linked Data	Google's preferred structured data format	Use JSON-LD for all structured data
Schema @type	The schema.org type (WebPage, Product, etc.)	Enables specific rich result types	Use the most specific type applicable
Microdata	HTML attribute-based structured data (itemscope)	Alternative to JSON-LD, inline markup	JSON-LD preferred, but Microdata is valid

7. Open Graph & Social

Meta tags that control how your content appears when shared on social media platforms.

Metric	Description	Why Important	Recommendation
og:title	Open Graph title	Shown when shared on Facebook, LinkedIn, etc.	Set on every page
og:description	Open Graph description	Snippet on social platforms	100–200 characters, compelling
og:image	Preview image for social sharing	Visual content gets more engagement	Min. 1200x630px
og:type	Content type (website, article, product)	Categorization on platforms	"website" for homepage, "article" for posts
og:url	Canonical URL for social sharing	Prevents duplicate signals	Should match canonical URL
og:locale	Language and region	Audience targeting	Match page language (e.g., de_DE)
og:site_name	Website name	Branding	Set consistently across all pages
twitter:card	Twitter/X Card type	Controls preview format	"summary_large_image" for visual content
twitter:title	Title for Twitter/X shares	Twitter-specific optimization	Falls back to og:title if not set
twitter:description	Description for Twitter/X	Shown below the title	Keep under 200 characters
twitter:image	Preview image for Twitter/X	Visual impact in timeline	Min. 800x418px

8. Internationalization

Configuration for multilingual and multi-regional websites.

Metric	Description	Why Important	Recommendation
Hreflang Tags	<link rel="alternate" hreflang="...">	Tells search engines about language variants	Required for multilingual sites
x-default	Default language/region hreflang	Fallback for unmatched users	Include x-default for all hreflang sets
html lang	<html lang="..."> attribute	Primary language signal	Always set, use BCP-47 format
Content-Language	HTTP header language indication	Server-level language hint	Should match html lang

9. Performance

Page speed and resource efficiency metrics that affect user experience and rankings.

Metric	Description	Why Important	Recommendation
Response Time (TTFB)	Time to first byte in milliseconds	Affects user experience and rankings	Under 800ms, ideally under 200ms
Page Size	Total HTML document size	Large pages are slow to load	Keep HTML under 3MB
CSS Count	Number of external CSS files	Each file = HTTP request	Combine CSS, use critical CSS
JS Count	Number of external JavaScript files	Blocks rendering	Minimize scripts, use async/defer
Inline CSS/JS	Size of inline <style> and <script> blocks	Blocks parser	Keep critical CSS inline, minimize JS
Render Blocking	CSS/JS in <head> without async/defer	Delays First Contentful Paint	Use async/defer for non-critical scripts
Third-Party Scripts	Scripts from external domains	External dependencies add latency	Audit and minimize
Content-Encoding	Compression (gzip, brotli)	Reduces transfer size 60–80%	Enable Brotli or gzip
Cache-Control	HTTP caching directives	Enables browser caching	Set max-age for static resources

10. Security

HTTP security headers and HTTPS configuration.

Metric	Description	Why Important	Recommendation
HTTPS	Encrypted connection	Google ranking signal since 2014	All pages must use HTTPS
HSTS	Strict-Transport-Security header	Forces HTTPS	Set with long max-age
CSP	Content-Security-Policy	Prevents XSS attacks	Define strict policy
X-Frame-Options	Clickjacking protection	Prevents iframe embedding	DENY or SAMEORIGIN
X-Content-Type-Options	MIME sniffing protection	Prevents type confusion	Set to "nosniff"
Referrer-Policy	Referrer control	Privacy and security	"strict-origin-when-cross-origin"
Permissions-Policy	Browser feature restrictions	Controls device API access	Restrict unused APIs
CORS	Access-Control-Allow-Origin	Cross-origin resource sharing	Be restrictive, avoid wildcard

11. Site Structure

How your site's pages are organized and interconnected.

Metric	Description	Why Important	Recommendation
Crawl Depth	Click distance from start URL	Deep pages crawled less frequently	Important pages within 3 levels
Internal/External	Whether URL belongs to same domain	Internal pages get more priority	Focus on internal pages
Duplicate Content	Pages with identical content hash	Dilutes ranking signals	Use canonicals or consolidate
Orphan Pages	Internal pages with zero inbound links	May not be discovered	Add internal links to every page

12. Site Signals

Additional signals that indicate a well-maintained, professional website.

Metric	Description	Why Important	Recommendation
Favicon	<link rel="icon">	Branding in browser tabs	Include in multiple sizes
Apple Touch Icon	<link rel="apple-touch-icon">	iOS home screen bookmarks	180x180px
Web Manifest	<link rel="manifest">	PWA features	Add for progressive web apps
RSS/Atom Feed	Syndication feed link	Content distribution	Add for blogs and news
AMP	<link rel="amphtml">	Accelerated Mobile Pages	Optional, no longer required by Google

All Issue Checks

Complete list of all automated SEO checks performed after each crawl, grouped by category.

Content

Issue Type	Severity	Trigger
`missing_title`	Error	Page has no <title> tag
`title_too_long`	Warning	Title exceeds 60 characters
`title_too_short`	Warning	Title is under 30 characters
`missing_meta_description`	Warning	No meta description tag
`description_too_long`	Warning	Description exceeds 160 characters
`description_too_short`	Info	Description is under 70 characters
`missing_h1`	Warning	Page has no H1 tag
`multiple_h1`	Warning	Page has more than one H1 tag
`heading_hierarchy_skip`	Warning	Heading levels skipped (e.g. H1→H3)
`heading_no_h1_first`	Warning	First heading is not H1
`no_headings`	Warning	Page has content but no heading tags
`thin_content`	Warning	Word count under 200
`duplicate_title`	Warning	Same title on multiple pages
`duplicate_description`	Warning	Same description on multiple pages
`missing_meta_viewport`	Error	No viewport meta tag (mobile-first)
`missing_html_lang`	Warning	No html lang attribute

Technical

Issue Type	Severity	Trigger
`redirect_chain`	Warning	More than 2 redirect hops
`missing_canonical`	Info	Indexable page without canonical URL
`noindex_in_sitemap`	Error	Page has noindex but may be in sitemap
`js_dependent_page`	Info	Large page with very low word count (SPA)
`meta_refresh_redirect`	Warning	Meta refresh redirect detected
`soft_404`	Warning	Status 200 but title contains "not found" / "404"
`missing_charset`	Info	No charset defined
`url_too_long`	Info	URL exceeds 200 characters

Links

Issue Type	Severity	Trigger
`broken_link`	Error	Page returns HTTP 4xx or 5xx
`orphan_page`	Warning	Internal page with zero inbound internal links
`internal_nofollow`	Info	Internal link with rel="nofollow"

Images

Issue Type	Severity	Trigger
`missing_alt_text`	Warning	Image has no alt attribute
`large_image`	Info	Image exceeds 100KB
`no_next_gen_format`	Info	Image uses JPEG/PNG/GIF instead of WebP/AVIF
`missing_lazy_loading`	Info	Large image (>50KB) without lazy loading

Performance

Issue Type	Severity	Trigger
`slow_response`	Warning	Response time exceeds 3000ms
`large_page`	Warning	Page size exceeds 3MB
`no_compression`	Warning	No gzip/brotli content-encoding
`no_caching`	Info	No Cache-Control header
`render_blocking_resources`	Warning	More than 5 render-blocking resources
`too_many_scripts`	Info	More than 15 external JS files

Social

Issue Type	Severity	Trigger
`missing_og_tags`	Info	Missing og:title or og:image
`missing_twitter_card`	Info	No twitter:card meta tag

Security

Issue Type	Severity	Trigger
`not_https`	Error	Page served over HTTP
`missing_hsts`	Info	No Strict-Transport-Security header
`missing_csp`	Info	No Content-Security-Policy header
`missing_x_frame_options`	Info	No X-Frame-Options header
`missing_x_content_type_options`	Info	No X-Content-Type-Options header
`missing_permissions_policy`	Info	No Permissions-Policy header

Internationalization

Issue Type	Severity	Trigger
`hreflang_missing_xdefault`	Info	Hreflang tags present but no x-default

Structured Data & Site Signals

Issue Type	Severity	Trigger
`missing_structured_data`	Info	No JSON-LD or Microdata found
`missing_favicon`	Info	No favicon detected on homepage

Views & Features

Overview of the analysis views and interactive features available.

Crawl Results Tabs

Tab	Description
All URLs	Complete list of crawled pages with status, depth, title, word count, response time, links, indexability
Titles	Title tags with length analysis and issue flags (missing, too long, too short)
Descriptions	Meta descriptions with length analysis and issue flags
Headings	H1/H2 content with comprehensive heading hierarchy issue detection
Links	All discovered links with source, target, anchor text, type, follow status
Images	All images with alt text, format, size, lazy loading, srcset, decorative status
Redirects	Pages with redirects showing target, hop count, and full chain
Canonicals	Canonical URLs with self-referencing check and indexability
Hreflang	Hreflang data for multilingual pages
Structured Data	JSON-LD and Microdata blocks with type and preview
Social / OG	Open Graph and Twitter Card meta tags
Resources	CSS/JS file counts, inline sizes, render-blocking, third-party scripts
Performance	TTFB, page size, HTTPS, HTTP version, compression, caching
Security	All security headers (HSTS, CSP, X-Frame, etc.), HTTPS status
Issues	All detected SEO issues with page, category, type, severity

Graph View

Interactive visualization of the site's internal link structure. Available from the crawl results page.

Feature	Description
Layout modes	URL Structure (radial tree from URL paths, like sitemap), Discovery Tree (how the crawler found pages), All Links (force-directed with all unique links)
Color by metric	18 metrics: Depth, Status, TTFB, Words, Size, Inlinks, Issues, Errors, Indexable, HTTPS, Meta Desc, H1, OG Tags, Schema, Text Ratio, Render Block, JS, CSS
Color thresholds	Configurable good/bad thresholds via settings panel (gear icon). Persisted in browser localStorage. Green = good, yellow = warning, red = bad
Size by metric	Node size scaled by Inlinks, Word Count, Outgoing Links, Page Size, or Fixed
Interaction	Hover to highlight connected nodes/edges, click to open page profile, zoom/pan, drag nodes

Page Profile

Detailed view of a single crawled page. Click any URL in the results or graph to open it.

Section	Description
Overview Stats	Status code, depth, word count, response time, page size, indexability
Issues	All issues detected for this specific page
On-Page SEO	Title, description, robots, canonical, viewport, lang, charset
Headings	Table view + interactive hierarchy graph showing heading structure with issue annotations
Content Analysis	SEO checklist with 12 checks (title, description, H1, canonical, viewport, indexable, HTTPS, content depth, OG, structured data, response time, compression)
Links	Outgoing links (with type, int/ext, follow) + incoming internal links
Images	All images with format, size, lazy loading, srcset, decorative flags
Open Graph & Social	All OG and Twitter meta tags
Structured Data	JSON-LD blocks formatted as JSON
Technical	HTTPS, HTTP version, compression, caching, redirects, pagination
Resources	CSS/JS counts, inline sizes, render blocking, third-party script list
Site Signals	Favicon, Apple Touch Icon, Manifest, RSS, AMP
Security Headers	HSTS, CSP, X-Frame, X-Content-Type, Referrer-Policy, Permissions-Policy, CORS

Crawl Configuration

Settings available when starting a new crawl. Values are clamped to valid ranges.

Setting	Default	Min	Max	Description
Max Pages	1,000	1	100,000	Maximum number of pages to crawl. Crawl stops when this limit is reached.
Max Depth	10	1	50	Maximum link depth from the start URL. Pages deeper than this are not followed.
Delay (ms)	500	100	60,000	Minimum delay between requests to the same domain. Lower = faster but more server load. Minimum 100ms enforced.
Concurrency	10	1	50	Number of parallel worker tasks. Only effective across multiple domains; single-domain crawls are limited by the delay setting.
Respect robots.txt	Yes	—	—	Whether to obey robots.txt crawl directives and crawl-delay.
Follow External	No	—	—	Whether to follow links to other domains (external pages).

Issue Severity Levels

SEO Crawler classifies issues by severity to help you prioritize fixes.

Severity	Meaning	Action
Error	Critical issues that likely prevent indexing or cause major problems	Fix immediately
Warning	Issues that could negatively impact rankings or user experience	Fix soon, prioritize by impact
Info	Optimization opportunities and best practice recommendations	Address when possible, lower priority