VercatusKnowledge base
The evidence behind every play.
The published library contains 187 source-backed entries, counted as of 12 October 2026. Each states a claim Vercatus plays rest on, about website access, content or citations, with its evidence grade and when it applies.
Published, graded, re-checked
Rules R-001 to R-195
A grade describes the provenance of an entry's sources, not the chance that a change will work. Entries whose sources have not been located at source are held back.
Browse
by topic.
Each topic page says what the category covers, how strong its evidence is, and lists every entry in it.
- 18 entries
Access and crawlers
What decides whether a crawler is allowed to fetch the page at all: the tokens named in robots.txt, the control each vendor publishes for its own crawler, and what a server, CDN or bot manager does when one knocks.
Open the topic - 27 entries
Agent readiness
What an AI agent needs to act on the site for a buyer: machine-readable offers and policies, checkout protocols, signed agents on purchase paths, forms it can fill, and tools it can call.
Open the topic - 25 entries
Answer engines
How the answer engines themselves behave: what each surface shows, how often, and how a source ends up named in an answer.
Open the topic - 12 entries
Commercial
Buying questions and the machinery behind them: prices and offers stated so they can be quoted, product feeds, reviews, and the protocols an agent uses to transact.
Open the topic - 11 entries
Content
How the page states its answer: headings and structure, freshness, internal links, images, and the words a snippet is taken from.
Open the topic - 8 entries
Entities
How a name is reconciled with the thing it names: identifiers, profiles, and the markup that ties an organisation, a person or a product to a record an engine already holds.
Open the topic - 7 entries
Languages and regions
Which version of a page belongs to which reader, how a system is told, and whether the translations agree with one another.
Open the topic - 10 entries
Measurement
How an effect is observed rather than assumed: which data source shows what, how late it arrives, and what it cannot tell you.
Open the topic - 13 entries
Performance
How quickly the page is served and drawn, which part of that an AI crawler ever sees, and where the measurement behind a threshold comes from.
Open the topic - 13 entries
Policies
The published rules that decide whether a page is treated as genuine: the search engines' own spam and quality policies, and the practices they name.
Open the topic - 9 entries
Retrieval
What happens after the page is read: how it is split, ranked and chosen, and which passage a system ends up quoting.
Open the topic - 29 entries
Technical
How the page is served and built: status codes, canonicals, crawl budget, rendering, sitemaps and the limits an engine applies before it reads a word.
Open the topic - 5 entries
Trust and provenance
Who stands behind a page: the pages that say who you are, provenance signals for media, and the higher bar for subjects that affect health or money.
Open the topic Search all 187 entries
Filter by topic and evidence grade, or search titles and claims.
SearchHow the base is curated
Sources re-fetched on a schedule; entries confirmed, updated or retired.
Read the docs
Search
every entry.
Narrow by topic and evidence grade, or search titles, claims and rule ids. The filters are kept in the address, so a filtered list can be shared.
187 entries
No entries match these filters. to see everything; your search text is kept.
- CWhy an agent browser can resemble ordinary browser trafficAccess and crawlers · re-check due 2027-03R-016
- AAI crawler names and the purposes they serveAccess and crawlers · re-check due 2027-03R-003
- AAdditional AI crawler tokens documented in 2026Access and crawlers · re-check due 2027-03R-021
- ACrawler tokens used by other AI vendorsAccess and crawlers · re-check due 2027-03R-014
- ADraft standards for content-use preferencesPolicies · re-check due 2027-03R-022
- ABing and Copilot content-preview controlsAccess and crawlers · re-check due 2027-06R-011
- ABrowser agent interaction semanticsAgent readiness · re-check due 2027-03R-013
- AWhen ChatGPT may show a blocked URL as a navigation linkAccess and crawlers · re-check due 2027-03R-017
- AHow Claude retrieves web pagesAccess and crawlers · re-check due 2027-06R-020
- ACloudflare controls for AI crawler accessAccess and crawlers · re-check due 2027-03R-005
- AContent signals policyAccess and crawlers · re-check due 2027-03R-001
- AGoogle agent and non-search crawler controlsAccess and crawlers · re-check due 2027-06R-019
- AGoogle Search controls for generative AI featuresAccess and crawlers · re-check due 2026-12R-010
- AHow to verify a genuine Googlebot requestAccess and crawlers · re-check due 2027-06R-004
- ANLWeb and schema endpointsAgent readiness · re-check due 2027-03R-008
- AOpenAI AdsBotAccess and crawlers · re-check due 2027-03R-009
- AOpenAI cloud browser signed requestsAccess and crawlers · re-check due 2027-03R-015
- APaywall markup and crawler accessAccess and crawlers · re-check due 2027-06R-012
- CEvidence and disputed claims about Perplexity crawlingAccess and crawlers · re-check due 2027-03R-018
- ARsl licensing standardPolicies · re-check due 2027-06R-023
- AWhat Search Console reports about AI visibilityMeasurement · re-check due 2027-03R-007
- ATDM reservation EUAccess and crawlers · re-check due 2027-09R-002
- AHow user-requested AI fetches differ from crawlingAccess and crawlers · re-check due 2027-03R-006
- AAcp agentic checkout endpointsAgent readiness · re-check due 2027-03R-025
- AAcp product feed fieldsAgent readiness · re-check due 2027-03R-024
- ACaptcha on action pathAgent readiness · re-check due 2027-03R-040
- AForm input purposeAgent readiness · re-check due 2027-09R-039
- AGoogle agentic checkout buy for meAgent readiness · re-check due 2027-03R-030
- AGoogle native commerce checkout eligibilityAgent readiness · re-check due 2027-03R-028
- AMachine payments HTTP 402Agent readiness · re-check due 2027-03R-034
- CMastercard agent pay acceptanceAgent readiness · re-check due 2027-03R-032
- AMCP remote serverAgent readiness · re-check due 2027-03R-042
- AMerchant center conversational attributesAgent readiness · re-check due 2027-03R-029
- AOffer state machine readableAgent readiness · re-check due 2027-06R-035
- CRaw HTML price and actionAgent readiness · re-check due 2026-12R-041
- AReturn shipping policy markupAgent readiness · re-check due 2027-06R-037
- ASchema actions unconfirmed consumersAgent readiness · re-check due 2027-06R-036
- ASigned agents on purchase pathsAgent readiness · re-check due 2027-03R-033
- AStripe shared payment tokensAgent readiness · re-check due 2027-03R-026
- ASubscription price markupAgent readiness · re-check due 2027-06R-038
- AUcp well known profileAgent readiness · re-check due 2027-03R-027
- AVisa trusted agent protocolAgent readiness · re-check due 2027-03R-031
- AWebmcp page toolsAgent readiness · re-check due 2027-03R-043
- AAgent payments protocolAgent readiness · re-check due 2027-03R-063
- AAgentic commerce protocol OpenAIAgent readiness · re-check due 2027-03R-061
- ALocal business profile and schemaCommercial · re-check due 2027-03R-064
- AMerchant center feeds power AI shoppingCommercial · re-check due 2027-06R-062
- CPricing passages with their commercial conditionsCommercial · re-check due 2027-03R-066
- AReview markup rulesCommercial · re-check due 2027-06R-065
- AUniversal commerce protocolAgent readiness · re-check due 2027-03R-060
- AAI generated product content labelsCommercial · re-check due 2027-06R-183
- CComparison intentsCommercial · re-check due 2027-03R-068
- AFAQ HowTo limitsCommercial · re-check due 2027-06R-069
- AIncentivized review disclosureCommercial · re-check due 2027-06R-182
- AProduct category markupCommercial · re-check due 2027-06R-184
- AProduct facts structuredCommercial · re-check due 2027-06R-067
- AIdentifying the correct product variantCommercial · re-check due 2027-06R-070
- ASale prices with accurate validity conditionsCommercial · re-check due 2027-06R-071
- AAnchor text signalContent · re-check due 2027-06R-079
- AAuthor experienceContent · re-check due 2027-06R-082
- AFreshness signalsContent · re-check due 2027-06R-081
- AHelpful people firstContent · re-check due 2027-06R-072
- AImage alt multimodalContent · re-check due 2027-06R-080
- AInternal links that connect related answersContent · re-check due 2027-06R-078
- AMeta descriptions and search snippet selectionContent · re-check due 2027-06R-077
- DOriginal data that readers can check and citeContent · re-check due 2027-09R-083
- BSelf contained passagesContent · re-check due 2027-06R-074
- AThin pagesContent · re-check due 2027-06R-073
- ADistinct page titles and clear topic ownershipContent · re-check due 2027-06R-076
- AApple maps business listingEntities · re-check due 2027-03R-187
- CFinding contradictory claims about the same entityEntities · re-check due 2027-09R-088
- DA defining page for each important entityEntities · re-check due 2027-06R-087
- AOrganization homeEntities · re-check due 2027-06R-085
- APerson authorsEntities · re-check due 2027-06R-089
- AsameAs links that identify the same organization or personEntities · re-check due 2027-06R-086
- AStructured data disambiguationEntities · re-check due 2027-06R-084
- AAgent surfacesAgent readiness · re-check due 2027-09R-102
- CEvidence on earned-media sources in AI citationsAnswer engines · re-check due 2027-03R-049
- BA study of citations to AI-generated documentationAnswer engines · re-check due 2027-09R-048
- CReported Google AI Mode adoption in 2026Answer engines · re-check due 2027-03R-050
- CEvidence on when AI Overviews appear in 2026Answer engines · re-check due 2027-03R-044
- CEvidence on visits to pages cited in AI OverviewsAnswer engines · re-check due 2027-03R-046
- CHow faithfully AI Overviews represent source claimsAnswer engines · re-check due 2027-03R-047
- CEvidence on AI Overviews and organic click-through rateAnswer engines · re-check due 2027-03R-045
- CAI overview top10 overlapAnswer engines · re-check due 2027-03R-097
- DWhy AI-influenced visits can be hard to attributeMeasurement · re-check due 2027-03R-054
- CReported consumer trust in AI search in 2026Answer engines · re-check due 2027-03R-052
- CEvidence on corroborating brand mentions across sourcesAnswer engines · re-check due 2027-03R-103
- AChatGPT search and fetchersAnswer engines · re-check due 2027-06R-056
- BCitations quotes statisticsAnswer engines · re-check due 2027-09R-094
- ACopilot uses Bing indexAnswer engines · re-check due 2027-03R-058
- CCrawler requests and referral visits measure different activityAnswer engines · re-check due 2027-03R-101
- ACrawler accessAnswer engines · re-check due 2027-03R-090
- CFreshness answer enginesAnswer engines · re-check due 2027-03R-100
- AGoogle preferred sources and personal contextAnswer engines · re-check due 2027-03R-059
- CInformation agents and agentic bookingAnswer engines · re-check due 2027-03R-051
- Allms txtAnswer engines · re-check due 2027-03R-099
- AGoogle AI search does not require special AI markupAnswer engines · re-check due 2027-06R-098
- APerplexity sources and freshnessAnswer engines · re-check due 2027-06R-057
- BQuery fan outAnswer engines · re-check due 2027-03R-096
- ASearch crawlers and training bots have different purposesAnswer engines · re-check due 2027-03R-091
- AWhy AI crawler blocking depends on firewall configurationAnswer engines · re-check due 2027-03R-092
- AAuthenticated identity for web botsAgent readiness · re-check due 2027-03R-093
- CBaseline evidence on searches without external clicksAnswer engines · re-check due 2027-03R-053
- Ahreflang reciprocityLanguages and regions · re-check due 2027-06R-104
- ALanguage signalsLanguages and regions · re-check due 2027-06R-105
- BLanguage and locale mismatches in retrievalLanguages and regions · re-check due 2027-09R-107
- ARegional search featuresLanguages and regions · re-check due 2027-03R-189
- BKeeping translated facts and coverage alignedLanguages and regions · re-check due 2027-06R-106
- ABing AI performanceMeasurement · re-check due 2027-03R-111
- BSeparating observed changes from causal attributionMeasurement · re-check due 2027-09R-109
- BCitation support and completenessMeasurement · re-check due 2027-06R-113
- CCitation trackingMeasurement · re-check due 2027-03R-108
- AGrounding source attributionMeasurement · re-check due 2027-03R-112
- ASearch Console completeness and attribution limitsMeasurement · re-check due 2027-06R-114
- AEvidence for whether a page is indexedMeasurement · re-check due 2027-06R-115
- ASearch Console as first-party search evidenceMeasurement · re-check due 2027-06R-110
- CInitial HTML and AI crawler rendering limitsPerformance · re-check due 2026-12R-127
- ACLS image dimensionsPerformance · re-check due 2027-06R-121
- ACWV ranking signalPerformance · re-check due 2027-06R-117
- ACWV thresholdsPerformance · re-check due 2027-06R-116
- AField and lab performance measure different conditionsPerformance · re-check due 2027-06R-118
- AImage formats and sizingPerformance · re-check due 2027-06R-126
- AINP replaced fidPerformance · re-check due 2027-06R-119
- ALCP causesPerformance · re-check due 2027-06R-120
- BPage weight and crawlPerformance · re-check due 2027-03R-123
- ARender blockingPerformance · re-check due 2027-06R-122
- CSpeed and engagementPerformance · re-check due 2027-09R-128
- AText compressionPerformance · re-check due 2027-06R-125
- AThird party scriptsPerformance · re-check due 2027-06R-124
- ABack button hijackingPolicies · re-check due 2027-06R-137
- ACloaking and hidden textPolicies · re-check due 2027-06R-134
- AExpired domain abusePolicies · re-check due 2027-06R-132
- AHelpful content in corePolicies · re-check due 2027-06R-135
- ALink spam and paid linksPolicies · re-check due 2027-06R-133
- CPublisher content licensing marketsPolicies · re-check due 2027-03R-191
- AReviews systemPolicies · re-check due 2027-06R-136
- AScaled content abusePolicies · re-check due 2027-06R-130
- ASite reputation abusePolicies · re-check due 2027-03R-131
- ASpam covers AI answersPolicies · re-check due 2027-03R-129
- ASpam reports manual actionPolicies · re-check due 2027-06R-192
- BChunking: structure and context matter more than sizeRetrieval · re-check due 2027-06R-140
- BEnough context for a passage to answer the questionRetrieval · re-check due 2027-09R-146
- BCross encoder rerankingRetrieval · re-check due 2027-09R-144
- CRepeated passages and ambiguous answer ownershipRetrieval · re-check due 2027-06R-143
- CEntity explicitnessRetrieval · re-check due 2027-06R-141
- BHybrid lexical denseRetrieval · re-check due 2027-06R-138
- BLost in the middleRetrieval · re-check due 2027-09R-139
- CMarkdown and tablesRetrieval · re-check due 2027-06R-145
- BSpecific numbers, dates and conditions in answer passagesRetrieval · re-check due 2027-09R-142
- AAmp host pagesTechnical · re-check due 2027-06R-195
- AHow canonical URLs and hreflang work togetherLanguages and regions · re-check due 2027-06R-159
- AConsistent canonical signals across the siteTechnical · re-check due 2027-06R-165
- ACrawl budget signalsTechnical · re-check due 2027-06R-158
- ACrawl rate server speedTechnical · re-check due 2027-06R-168
- ACWV tiebreakerTechnical · re-check due 2027-06R-169
- ADiscover core update 2026Technical · re-check due 2027-03R-193
- ADiscover eligibilityTechnical · re-check due 2027-06R-155
- AFaceted navigationTechnical · re-check due 2027-06R-149
- AGEO targeting and currencyLanguages and regions · re-check due 2027-06R-160
- AGoogle news automatic inclusionTechnical · re-check due 2027-06R-194
- AHTML size limitsTechnical · re-check due 2027-03R-167
- AHTTPS and interstitialsTechnical · re-check due 2027-06R-151
- AIndexing API scopeTechnical · re-check due 2027-06R-154
- AIndexNowTechnical · re-check due 2027-03R-172
- AJavaScript challenges can hide the intended pageTechnical · re-check due 2027-06R-163
- ALazy loading and hidden contentTechnical · re-check due 2027-06R-150
- AMobile firstTechnical · re-check due 2027-06R-170
- APagination and infinite scrollTechnical · re-check due 2027-06R-148
- CUseful content in initial HTML for AI crawlersTechnical · re-check due 2026-12R-161
- ARedirect chainsTechnical · re-check due 2027-06R-166
- ARendering budgetTechnical · re-check due 2027-06R-162
- Arobots meta directivesTechnical · re-check due 2027-06R-157
- Arobots RFCTechnical · re-check due 2027-06R-171
- ASite moves and redirect signalsTechnical · re-check due 2027-06R-152
- ASitemaps containing current indexable canonical URLsTechnical · re-check due 2027-06R-164
- ASnippet controlsTechnical · re-check due 2027-06R-173
- ASoft 404Technical · re-check due 2027-06R-147
- AStructured data types that matterEntities · re-check due 2027-06R-153
- AVideo and image indexingTechnical · re-check due 2027-06R-156
- AInitial noindex directives and later renderingTechnical · re-check due 2027-06R-175
- ASupported structured-data formats and their limitsTechnical · re-check due 2027-06R-174
- AAbout contact policiesTrust and provenance · re-check due 2027-06R-179
- CConsistency across webTrust and provenance · re-check due 2027-06R-180
- AContent credentials c2paTrust and provenance · re-check due 2027-03R-177
- BProvenance signalsTrust and provenance · re-check due 2027-03R-176
- AYMYL standardsTrust and provenance · re-check due 2027-06R-178
See which entries apply to your site.
Every play on your own domain cites the entries it rests on.
Cancel any time · Data stored in the EU