Perplexity is the strongest fit for pre-publication fact-checking because it searches the live web and returns cited sources alongside every answer, letting you trace each claim back to its origin quickly. You can paste a specific claim or question and get a sourced response rather than a generated guess, which is exactly what verification requires. Gemini Pro is a solid alternative when you want a capable LLM with Google Search grounding built in. Claude Sonnet works well if you need to reason carefully through complex or nuanced claims and want a thorough written analysis of the evidence you supply.