usefulweb.site AI Answer Verifier

Internet, AI & productivity

AI Answer Verifier

Split an AI answer into claims and see which ones your sources actually support.

Paste one or more sources. Separate sources with a line containing only ---

Public pages fetched once (max 5).

Try an example: Eiffel Tower facts · Wrong number

How it works

Paste an AI-generated answer and the sources it should be based on (text or public URLs). Each sentence becomes a claim; check-worthy claims (numbers, dates, names, superlatives, causes) are flagged, and every claim is matched to the best-supporting source sentence with BM25 scoring and number checks.

  • Claims = sentences of the answer with at least 15 characters.
  • Check-worthy if the claim contains numbers, years, multi-word proper names, superlatives/absolutes or causal wording.
  • Each source is split into sentences; the best match for a claim is the source sentence with the highest BM25 score (k1 = 1.2, b = 0.75) over content words.
  • Coverage = share of the claim's distinct content words found in that sentence. supported: coverage ≥ 0.7 and every number in the claim appears in it; partially-supported: coverage ≥ 0.4; contradicted-number: coverage ≥ 0.5, a number from the claim is missing from the evidence and the evidence contains a different number; otherwise not-found.

This is lexical evidence matching, not truth verification: "supported" means similar wording exists in your sources, not that the sources are right. Paraphrases can be missed.

For scripts and AI agents

  • JSON API: POST https://aianswerverifier.usefulweb.site/api/v1/calculate (same calculation as this page)
  • Interface description: OpenAPI 3.1 · AI guide: llms.txt
  • MCP server (Streamable HTTP): https://aianswerverifier.usefulweb.site/mcp · tool name ai_answer_verifier
Example request
curl -s -X POST https://aianswerverifier.usefulweb.site/api/v1/calculate \
  -H 'content-type: application/json' \
  -d '{"answer":"The Eiffel Tower was completed in 1889 for the World's Fair in Paris. It is 330 metres tall. It was designed by Gustave Eiffel alone. It is the most visited paid monument in the world.","sources":"The Eiffel Tower was built for the 1889 World's Fair in Paris and completed in March 1889.\nIt is 330 metres (1,083 ft) tall, including antennas.\n---\nThe tower was designed by the engineers Maurice Koechlin and Émile Nouguier of Gustave Eiffel's company."}'

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