1. Confirmed Factors by Google

    1. BERT
    2. Crisis Information Systems
    3. Deduplication Systems
    4. Exact Match Domain 5
    5. Freshness Systems
    6. Helpful Content System
    7. Link Analysis Systems
    8. Local News Systems
    9. MUM
    10. Neural Matching
    11. Original Content Systems
    12. Removal-based Demotion System
    13. Page Experience System
    14. Passage Ranking System
    15. Product Review System
    16. RankBrain
    17. Reliable Information Systems
    18. Site Diversity System
    19. Spam Detection Systems

  2. Domain Factors

    1. Domain Age
    2. Domain Name
    3. Keyword in Domain Name
    4. Domain Registration Length
    5. Keyword in Subdomain
    6. Domain History
    7. Exact Match Domain
    8. Public Vs. Private WhoIs
    9. Penalized WhoIs Owner
    10. Country TLD Extension

  3. Special Google Algorithm Rules

    1. Query Deserves Freshness
    2. Query Deserves Diversity
    3. User Browsing History
    4. User Search History
    5. Featured Snippets
    6. Geo-Targeting
    7. Safe Search
    8. “YMYL” Keywords
    9. DMCA Complaints
    10. Domain Diversity
    11. Transactional Searches
    12. Local Searches
    13. Top Stories Box
    14. Big Brand Preference
    15. Shopping Results
    16. Image Results
    17. Easter Egg Results
    18. Single Site Results for Brands
    19. Payday Loans Update

  4. Brand Signals

    1. Branded Anchor Text
    2. Branded Search
    3. Facebook Page and Likes
    4. Brand + Keyword Searches
    5. Twitter Profile with Followers
    6. Official LinkedIn Company Page
    7. Known Authorship
    8. The Legitimacy of Social Media Accounts
    9. Brand Mentions on Top Stories
    10. Unlinked Brand Mentions
    11. Brick and Mortar Location

  5. Page-Level Factors

    1. Keyword in Title Tag
    2. Title Tag Starting with Keyword
    3. Keyword in Description
    4. Keyword in H1 Tag
    5. TF-IDF
    6. Content-Length
    7. Table of Contents
    8. Keyword Density
    9. LSI in Content (LSI)
    10. LSI Keywords in Tags
    11. Page Covers Topics In-Depth
    12. Page Loading Speed via HTML
    13. Page Loading Speed Via Chrome
    14. Use of AMP
    15. Entity Match
    16. Google Hummingbird
    17. Duplicate Content
    18. Rel=Canonical
    19. Image Optimization
    20. Content Recency
    21. The Magnitude of Content Updates
    22. Historical Page Updates
    23. Keyword Prominence
    24. Keyword in H2, H3 Tags
    25. Outbound Link Quality
    26. Outbound Link Theme
    27. Grammar and Spelling
    28. Syndicated Content
    29. Mobile-Friendly Update
    30. Mobile Usability
    31. Hidden Content on Mobile
    32. Helpful “Supplementary Content”
    33. Content Hidden Behind Tabs
    34. Number of Outbound Links
    35. Relevant Images
    36. Number of Internal Links
    37. Quality of Internal Links
    38. Broken Links
    39. Reading Level
    40. Affiliate Links
    41. HTML Errors/W3C Validation
    42. Domain Authority
    43. Page’s PageRank
    44. URL Length
    45. URL Path
    46. Human Editors
    47. Page Category
    48. Keyword in URL
    49. URL String
    50. References and Sources
    51. Bullets and Numbered Lists
    52. Priority of Page in Sitemap
    53. Too Many Outbound Links
    54. UX Signals From Other Keywords
    55. Page Age
    56. User-Friendly Layout
    57. Parked Domains
    58. Useful Content
    59.  

  6. User Interaction

    1. RankBrainTime
    2. Organic CTR for A KeywordTime
    3. Organic CTR for All KeywordsTime
    4. Bounce RateTime
    5. Direct TrafficTime
    6. Repeat TrafficTime
    7. Pogo StickingTime
    8. Blocked SitesTime
    9. Chrome BookmarksTime
    10. Number of CommentsTime
    11. Dwell Time

  7. On-Site Webspam Factors

    1. Panda Penalty
    2. Links to Bad Neighborhoods
    3. Redirects
    4. Pop-ups
    5. Interstitial Pop-Ups:
    6. Site Over-Optimization
    7. Gibberish Content
    8. Doorway Pages
    9. Ads Above the Fold
    10. Hiding Affiliate Links
    11. Fred
    12. Affiliate Sites
    13. Auto-Generated Content
    14. Excessive PageRank Sculpting
    15. Meta Tag Spamming
    16. IP Address Flagged as Spam

  8. Off-Site Webspam Factors

    1. Hacked Sites 
    2. Unnatural Influx of Links
    3. Penguin Penalty 
    4. Link Profile with a High Percentage of Low-Quality Links
    5. Links From Unrelated Sites
    6. Unnatural Links Warning
    7. Low-Quality Directory Links
    8. Widget Links 
    9. Links from the Same Class C IP
    10. “Poison” Anchor Text
    11. Unnatural Link Spikes
    12. Links From Articles and PR
    13. Manual Actions
    14. Selling Links
    15. Google Sandbox
    16. Google Dance
    17. Disavow Tool
    18. Reconsideration Request
    19. Temporary Link Schemes

  9. Site-Level Factors

    1. Content Providing Value and Unique Insights
    2. Contact Us Page
    3. Domain Trust / TrustRank
    4. Site Architecture
    5. Presence of Sitemap
    6. Site Uptime
    7. Server Location
    8. SSL Certificate
    9. Terms of Service & Privacy Pages
    10. Duplicate Meta Information On-Site
    11. Breadcrumb Navigation
    12. Mobile-Optimized
    13. YouTube
    14. Site Usability
    15. Using GA and GSC
    16. User reviews/Site reputation

  10. Backlink Factors

    1. Linking Domain Age
    2. Number of Linking Root Domains
    3. Number of Links from Separate C-Class IPs
    4. Number of Linking Pages
    5. Backlink Anchor Text
    6. Alt Tag (for Image Links)
    7. Links from .edu or .gov Domains
    8. Authority of Linking Page
    9. Authority of Linking Domain
    10. Links from Competitors
    11. Links from “Expected” Websites
    12. Links from Bad
    13. Neighborhoods
    14. Guest Posts
    15. Links from Ads
    16. Homepage Authority
    17. NoFollow Links
    18. Diversity of Link Types
    19. “Sponsored” or “UGC” Tags
    20. Contextual Links
    21. Excessive 301 Redirects to Page
    22. Internal Link Anchor Text
    23. Link Title Attribution
    24. Country TLD of Referring Domain
    25. Link Location In Content
    26. Link Location on Page
    27. Linking Domain Relevancy
    28. Keyword in Title
    29. Page-Level Relevancy
    30. Positive Link Velocity
    31. Negative Link Velocity
    32. Links from Hubpages
    33. Link from Authority Sites
    34. Linked to as Wikipedia Source
    35. Co-Occurrences
    36. Backlink Age
    37. Links from Real Sites vs. “Splogs”
    38. Natural Link Profile
    39. Reciprocal Links
    40. User-Generated Content Links
    41. Links from 301
    42. Number of Outbound Links Within a Page
    43. Forum Links
    44. Word Count of Linking Content
    45. Schema.org Usage
    46. TrustRank of Linking Site
    47. Sitewide Links
    48. Quality of Linking Content

  11. Retired Ranking System

    1. Hummingbird
    2. Mobile-friendly Ranking System
    3. Page Speed System
    4. Panda System
    5. Penguin System
    6. Secure Site System