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Tools solve the task in front of you. These pages explain why it works, so next time you already know. Free, no sign-up, and nothing you read or type leaves your browser.
Unravel: understand Java code
Paste Java, open a file or import it from GitHub. Unravel names the concepts first, draws the flow, then walks through it step by step at the detail level you pick. The explanations use no AI by default, and nothing is uploaded unless you turn on the optional AI mode.
Java concept library (267)
Kafka offsets, Spring proxies, streams, concurrency, JPA and more, each with a mental model, how it works, the usual mistakes and what happens inside.
Learning paths (32)
Ordered routes through the concepts so every idea builds on the one before. Mark steps as learned; progress stays in your browser.
Java exceptions (40)
What each exception means, the usual causes, how to fix it, and a short example. The page you land on when you search the error text.
Cron guides
The symbols (?, L, W, # and /) in plain English, fixes for common cron errors, and a library of ready-made schedules for every dialect.
Daily cron quiz
Five fresh questions every day. A few minutes of practice that makes you faster at reading schedules, with a streak to keep you honest.
Time zone pages
Convert between popular zones with real daylight-saving dates, conversion tables and the best meeting hours.
📚 Cheat sheets
Quick references for the thing you can never quite remember.
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