How do I find out what is costing money in my S3 bucket?

The three reports

• Cost Explorer, the cost report. Filter to S3 and group by usage type. Rent, fetches, downloads and archive retrievals show up as separate lines, so you can see which half of the bill you are in.
• CloudWatch, the metrics page. The size of every bucket, once a day, by shelf.
• Storage Lens, the storage report. Free at its default level, and the only one that shows how much space hidden old versions and half-finished uploads take.

What they cannot tell you

None of them knows whether anyone opens the files. That needs server access logging, a who-opened-what log, switched on for a few weeks, or a tool that samples the files and reads when each was last touched.

$0

S3 Savings: three months of your real bill, every bucket, the hidden lines, and an estimate of how much nobody has opened

It only reads. Applying a change needs your approval, every time.