Use "ultrathink" to Unlock Maximum Reasoning
The ultrathink keyword instructs Claude to spend its maximum internal reasoning budget before responding — significantly more deliberate than a standard reply.
ultrathink
I have a race condition in my distributed job queue where two workers
occasionally process the same job. The queue uses Redis LPOP. Explain
exactly what's happening and propose a fix using atomic Redis operations.
Claude will spend significantly more tokens reasoning through the problem before giving you an answer — useful for architecture decisions, subtle bugs, and complex algorithm design where a fast answer is worse than a thoughtful one.
The reasoning hierarchy goes from lightest to heaviest:
think → think hard → think harder → ultrathink
Each step allocates more internal reasoning budget. For everyday questions the default is fine, but when you're stuck on something genuinely complex, prepending ultrathink to your prompt often catches angles a quick response misses.
Use it sparingly — the extra reasoning takes more time and tokens. Reserve it for the problems that have kept you stuck for hours, not the ones you could solve with a quick search.
Save ultrathink for the problems that actually deserve it — it's worth the wait.
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Before jumping to implementation, describe the problem conversationally and let Claude be your thinking partner. It asks clarifying questions, surfaces tradeoffs you haven't considered, suggests approaches, and pokes holes in your plan — so by the time you say "ok, build it," both of you know exactly what to build and why.
Paste error messages with "why did this fail?" instead of "fix this" to get Claude to diagnose the root cause before applying a fix.
When you need Claude to make changes in one area without affecting another, add negative constraints — "fix the bug but don't change the public API", "refactor the internals but don't create new files", or "update the logic but don't modify any tests." Explicit exclusions prevent Claude from making well-intentioned changes you'll have to undo.