Authoritative Web Standards Reference

Web Performance & Technical SEO Glossary

Clear definitions, official W3C and Google Web Vitals thresholds, syntactical directives, common developer pitfalls, and actionable auditing guidance for modern web engineers.

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Showing 16 terms

A

1

Accessibilityalt="..."

Alternative Text

Alternative text (alt text) is a descriptive HTML attribute (alt="...") applied to <img> tags that provides a textual equivalent for visual imagery to assist screen readers and search crawlers.

Full Definition & Auditing Rules

C

5

Core Web Vitals & SpeedCLS

Cumulative Layout Shift

Cumulative Layout Shift (CLS) measures visual stability by aggregating the unexpected layout shifts that occur across a page's entire lifecycle during user viewing and navigation.

Full Definition & Auditing Rules

Technical SEOrel="canonical"

Canonical URL

A canonical URL is an HTML link element (<link rel="canonical" href="...">) that specifies the authoritative, primary master URL among multiple duplicate or near-duplicate pages on the web.

Full Definition & Auditing Rules

Security & PrivacyCSP

Content Security Policy

A Content Security Policy (CSP) is an HTTP response header or HTML meta tag that restricts the origins and resources (scripts, images, stylesheets, fonts, iframes) the browser is permitted to load and execute.

Full Definition & Auditing Rules

Core Web Vitals & SpeedCWV

Core Web Vitals

Core Web Vitals (CWV) are Google's standardized metrics quantifying real-world web user experience: Largest Contentful Paint (LCP) for loading speed, Interaction to Next Paint (INP) for responsiveness, and Cumulative Layout Shift (CLS) for visual stability across all device form factors.

Full Definition & Auditing Rules

Technical SEO & IndexingCrawl Budget

Crawl Budget

Crawl budget is the total number of URLs that search engine bots, such as Googlebot, can and intend to crawl on a given website within a specific timeframe based on server capacity and site authority.

Full Definition & Auditing Rules

F

1

Core Web Vitals & SpeedFCP

First Contentful Paint

First Contentful Paint (FCP) measures the time elapsed from page navigation until the browser renders the first piece of DOM content, such as text, images, SVG graphics, or non-white canvas elements.

Full Definition & Auditing Rules

H

1

Technical SEO & Indexingrel="alternate" hreflang

Hreflang Annotation

Hreflang is an HTML link attribute specification that informs search engines about the specific geographic region and language targeted by alternate localized versions of a webpage to serve the correct regional URL to users.

Full Definition & Auditing Rules

I

1

Core Web Vitals & SpeedINP

Interaction to Next Paint

Interaction to Next Paint (INP) is a Core Web Vital metric that measures overall page responsiveness by assessing the latency of all discrete user interactions (clicks, taps, keypresses) throughout the session.

Full Definition & Auditing Rules

L

1

Core Web Vitals & SpeedLCP

Largest Contentful Paint

Largest Contentful Paint (LCP) is a Core Web Vital metric measuring the time from initial page navigation until the largest visual content element within the user's viewport is fully rendered.

Full Definition & Auditing Rules

R

1

Technical SEOrobots.txt

Robots Exclusion Protocol

A robots.txt file is a plain text document positioned at the root directory of a domain that instructs search engine web crawlers which URLs and directories they are permitted or forbidden to request.

Full Definition & Auditing Rules

S

1

Technical SEO & IndexingSchema.org / JSON-LD

Structured Data

Structured data is a standardized format using Schema.org vocabularies and JSON-LD syntax to explicitly annotate web page content, allowing search engine algorithms to disambiguate entities and generate rich search result enhancements.

Full Definition & Auditing Rules

T

2

Core Web Vitals & SpeedTTFB

Time to First Byte

Time to First Byte (TTFB) is the foundational latency metric measuring the duration from the moment the browser initiates an HTTP request until the first byte of response data is received from the web server.

Full Definition & Auditing Rules

Core Web Vitals & SpeedTBT

Total Blocking Time

Total Blocking Time (TBT) is a lab performance metric measuring the cumulative duration between First Contentful Paint (FCP) and Time to Interactive (TTI) where the browser main thread was blocked by tasks exceeding 50 ms.

Full Definition & Auditing Rules

W

1

AccessibilityWCAG

Web Content Accessibility Guidelines

Web Content Accessibility Guidelines (WCAG) is the internationally recognized technical standard developed by the W3C Web Accessibility Initiative (WAI) to make web content accessible to people with disabilities.

Full Definition & Auditing Rules

X

1

Technical SEOsitemap.xml

XML Sitemap

An XML sitemap is a structured XML protocol file listing all authoritative, indexable URLs on a website along with metadata (last modification date, change frequency) to facilitate search engine discovery.

Full Definition & Auditing Rules

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