Short answer — the single most accurate sources are the airline/program websites themselves (United, American, Air Canada/Aeroplan, ANA, etc.), followed by ExpertFlyer for fare‑class/award inventory when it supports the carrier. Aggregator/search engines (point.me, PointsYeah, Roame/Seats.aero, SeatSpy, etc.) are excellent for discovery and alerts but can be slower, incomplete, or show cached/stale results — always verify on the airline’s site or by phone. (thepointsguy.com)

Details and how to use them

• Airline/program websites (authoritative): Start searches on the carrier you plan to book through (United, AA, Aeroplan, ANA, Air France/KLM, etc.). These show the live inventory for that program and are the definitive source for whether a seat is bookable. Use different programs for cross‑checking partner space (e.g., Aeroplan/ANA/United for Star Alliance). (thepointsguy.com)

• ExpertFlyer: Historically one of the most accurate third‑party tools for fare‑class and award availability and very useful for alerts — but note it doesn’t cover every airline and has had periods where access to many carriers was lost. If your airline is supported, ExpertFlyer is a top choice for precise availability data and alerts. (thepointsguy.com)

• Aggregators / award search engines (point.me, PointsYeah, Roame.Travel, etc.): Great for broad multi‑program searches, discovering routings and comparative pricing, and inspiration. Reviews and testing show they vary in coverage, speed, and accuracy — they’re best used to find options quickly, then verify/book on the airline site. (awardwallet.com)

• Visualization & calendar tools (Seats.aero, SeatSpy, etc.): Very handy for getting a one‑page or month view of availability. Their downside: some rely on periodic refreshes or caching, so results can be out of date or “last seen” rather than strictly live. Use them for spotting patterns, then confirm live. (nerdwallet.com)

Practical checklist

1. Search the airline/program site(s) that will actually issue the ticket (authoritative). (thepointsguy.com)
2. Use ExpertFlyer for alerts and fare‑class detail if the airline is supported. (thepointsguy.com)
3. Use aggregators (point.me, PointsYeah, Roame, etc.) for discovery and options you might miss. Verify any hit on the carrier that will issue the award. (awardwallet.com)
4. If an award shows online but won’t book, try calling the airline (and if needed, try again or ask a different agent) — sometimes inventory is viewable but requires phone ticketing. (thepointsguy.com)

If you want, I can give a short recommended toolkit for a typical U.S. traveler (which airline sites and which paid/free aggregators to pair together) based on your most‑frequent routes or alliances.