What each one actually offers for free, as plainly as we can put it.
chess.com and Lichess are both excellent, established platforms — this isn't about one being "better" overall, since they each do a lot beyond analysis (live play, tournaments, social features, communities) that See The Mate doesn't try to replace. This is specifically about what's free when it comes to post-game analysis, since that's the one thing all three offer and it's where the differences are actually meaningful.
chess.com's Game Review is polished and detailed, but on a free account it's historically been limited — typically to one full review per day, with deeper or unlimited analysis reserved for paid Diamond membership. It's a strong tool within that limit, but the limit itself is the thing to be aware of if you play more than one serious game a day and want to review each one.
Lichess is unusual in the chess world for offering completely free, unlimited engine analysis with no paywall at all — it's a nonprofit, ad-free platform, and this is one of the most player-friendly things about it. The analysis runs server-side but isn't rate-limited the way most commercial platforms are.
See The Mate is also fully free with no daily cap, but gets there differently — instead of a nonprofit absorbing server costs, the Stockfish engine runs directly in your own browser, so there's no server cost to absorb in the first place. In practice this means unlimited analysis, plus a puzzle trainer pulled from Lichess's own open puzzle database, opening detection via the Lichess Explorer, and move classification with the same centipawn-loss approach used across the industry.
chess.com and Lichess are both full platforms — you can play live games, join tournaments, and be part of an active community on either. See The Mate is intentionally narrower: it's an analysis and puzzle tool, not a place to play rated games against other people (yet — local two-player is supported today). Analysis speed on See The Mate depends on your own device rather than a dedicated server, so older phones will be slower than a fast laptop, whereas server-side analysis is consistent regardless of your device.
If you want live play, tournaments, and a broader chess community, chess.com and Lichess both do that well and See The Mate doesn't try to compete there. If what you specifically want is unlimited, in-depth, free post-game analysis and unlimited puzzle practice — without an account, a daily cap, or a paywall — that's exactly what See The Mate is built around.
Read more about the architecture behind this in Why Client-Side Chess Analysis Is Different.