Open-source flight search MCP server refuses to answer what it can't confirm, curbing model hallucination
Fast_Entrance7839 · reddit · 2026-11-13
A developer shared viajante, a free MIT-licensed flight and hotel search tool that runs locally as a CLI, Python library, and MCP server, scraping Google Flights, Google Hotels, and Booking.com without any API key.
The core design insight is anti-hallucination in MCP tool design—the tool should refuse to answer what it cannot verify, rather than leaving gaps the model fills with plausible-sounding guesses:
- Checked bags: refused entirely, since no data source confirms checked-bag pricing; carry-on pricing via Google stays.
- Currency: never converted; defaults to the origin airport's country currency if unspecified, and hotels always require an explicit one.
- Missing fields: anything Google doesn't show is omitted or marked unknown, leaving nothing for the model to turn into a "fact."
Try it with npx -y @viajante/mcp or uvx --from "viajante[mcp]" viajante-mcp (no Node needed). The author asks the community: when your server can't answer something, do you make the tool refuse, or leave it to the model?
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