01 · Free
Caffeine half-life calculator
Estimate how much caffeine may remain by bedtime, compare faster and slower clearance, and see every assumption behind the curve.
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Small tools. Visible assumptions. No miracle output.
Each tool answers one practical question, keeps the method beside the result, and links back to a deeper guide.
02 · Free
Baby-name shortlist builder
Browse verified place-and-year rankings, filter published fields, and keep a private shortlist in this browser.
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Pregnancy due-date calculator
Estimate a due date from LMP, cycle length, or IVF transfer, with the exact convention shown beside the result.
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