Second and final devlog (i think)
So this started as “what if a website could tell you why you missed” and got wildly out of hand. Everything below runs at retrace-osu.vercel.app now. Recap of the whole thing:
The replay engine: The core of the site. You drop a .osr and it gets decoded entirely in your browser, the beatmap is auto-fetched by its hash, and then a reconstruction engine re-judges the whole play from the raw cursor and key data: every circle, slider follow-circle and spinner spin. It handles note stacking, stable’s notelock behavior, and mod clock rates properly, and the reconstructed judgements come out within a hit or two of the real scoreboard numbers. From that you get UR, timing bias, early/late split, per-section breakdown, and pattern splits (jumps, streams, bursts, spaced control) that know the difference between a 180bpm stream and that same stream with DT on.
The autopsy tools: A replay viewer with the actual slider paths, approach circles, miss markers and cursor trail, that now works like a proper video editor: quarter speed, frame stepping, keyboard shortcuts, and clickable miss timestamps that jump you to two seconds before each choke. You can even load a second replay of the same map as a green ghost cursor and watch where your lines diverge. There’s a playfield miss map, a hands panel that tells you your k1/k2 split, whether you single-tap or alternate and at what bpm you give in and switch, and whether you snap or flow aim, all measured from the frames.
The coach: Every analysis ends with strengths, leaks and practice drills derived from the measurements, plus an AI review that gets fed only measured facts (mod-adjusted stars, real clock rate, strain curve) so it can’t hallucinate numbers. My favorite part is the difficulty overlay: it draws the map’s strain curve behind your per-section UR, so it can tell you whether you fall apart at the hard parts (skill wall) or the easy parts (focus problem). Those need completely different fixes and no other tool makes the distinction.
Farm maps: Sign in and it profiles your top 100: your real mod combos with each one’s median accuracy, your comfort star band, and your aim/speed lean measured with rosu-pp. Then it prices candidate maps under your actual mods at your actual accuracy and, this is the important bit, ranks them by the real gain to your weighted total, not the raw pp fantasy. A “400pp play” that nets you 0.6pp gets buried. There’s also a chokes tab that finds plays in your bests worth fixing, and a ceiling number showing your total if you cleaned all of them.
Informatics: Type any username: mod-combination picker over their top 100 (exact combos, HD means HD only), pp milestones, 90-day rank graph, and trivia like their oldest surviving play, their most farmed mapper, their grade split and how much of their profile one play carries. Countries get a top-50 deep scan: hidden prodigies by pp per hour, the “national anthem” (the map half the country has in their bests), the oldest relic score still standing, the closest rivalry (Pakistan has two players literally 0pp apart), scene depth, farm diversity. Plus a side-by-side player compare page.
History: Every analyzed replay saves to your browser, nothing uploaded. Bulk-drop your whole Replays folder and it aggregates: which weaknesses recur across your plays, your UR trend, and per-map progress when you’ve analyzed the same map more than once.
Everything else: osu!-style UI with the triangles, 30-day sessions with token refresh, PNG share cards, link embeds, installable as an app, and a disk cache so the osu! API doesn’t hate me.The whole thing is client-first: your replays never leave your machine, the server only does pp math and API relaying. Go break it and tell me what’s wrong.