VercatusGrounding source attribution
Answer engines expose two different things: the sources they retrieved or considered, and the sources a given passage of the answer is attributed to. Gemini's grounding metadata separates groundingChunks (the web sources, uri and title) from groundingSupports, each of which links a text segment (start and end index) to one or more chunk indices; a chunk without a support was retrieved but not attributed. Claude's web search tool likewise returns results (url, title, page_age) in web_search_tool_result blocks, while citations (web_search_result_location with url, title and up to 150 characters of cited_text) sit on the text blocks they support; citations are always enabled for web search. Retrieved, attributed and mentioned-by-name are three distinct states of visibility.
Sources
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- 2Claude Docs · 2026Web search tool (web_search_tool_result blocks and web_search_result_location citations)platform.claude.com
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AGrade A: official documentation or a standard. A grade describes the provenance of the sources above; it is not a probability that a change will work. The effect basis says how the size of the effect is known: measured by a study, taken from an industry report, only documented without a size, or not quantified.
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