DeepInquiry is a verified fact library and API service from Machine Accountability Corporation, designed to help AI systems and their users access factual claims with clear evidence and provenance. Its growing corpus includes more than 2,900 facts across topics such as science, history, nature, technology, culture, and world events. Before publication, claims are cross-checked against sources on different websites, dated, cited, and assigned confidence scores and verification tiers. The service groups related sources and sets aside known Wikipedia mirrors and aggregators when other source types are available.

DeepInquiry provides its facts through an API for retrieval-augmented generation, AI agents, and applications that need grounded, citable information. Each fact response includes source details, a score indicating source independence, a verification tier, and a CiteSig attestation. This Ed25519 cryptographic signature allows users to check that a claim and its sources have not been altered. Developers can access a free tier of 500 API requests per month, with additional API, data licensing, and Plus options also listed.