S3 Estate Calibration Auditor

Audit an estate of AWS S3 buckets for the one bucket that is genuinely publicly or cross-account exposed, without over-flagging the many buckets that READ as exposed but are neutralised. Resolves each bucket's EFFECTIVE verdict by composing four layers (Block Public Access x bucket policy x bucket ACL x access points), never one layer alone, then rolls the per-bucket verdicts up into an estate verdict. Its discipline is symmetric: BPA (RestrictPublicBuckets / BlockPublicPolicy) neutralises a Principal '*' policy but NOT a cross-account grant; IgnorePublicAcls kills a public-group ACL grant but NOT a cross-account canonical-user grant; a narrowing Condition (org id, ExternalId, SourceIp, access-point delegation) scopes a Principal '*' so it is not public. On a needle estate it names the ONE live bucket as the primary finding; on a clean estate it reports NO live exposure and does not manufacture findings. Then it states what the bucket configs alone cannot answer (per-object ACLs, CloudFront/CDN fronting, the trusted principals' identity policies, account-level BPA dependency, data sensitivity). Use when asked to review an S3 bucket fleet for public exposure, cross-account access, or whether the estate is clean. Vendor-neutral; runs offline against describe-bucket / get-bucket-policy / get-bucket-acl / list-access-points JSON with no Anyshift account.

mkdir -p ~/.claude/skills/s3-estate-calibration-auditor
curl -L https://claudskills.com/skills/s3-estate-calibration-auditor/SKILL.md \
  -o ~/.claude/skills/s3-estate-calibration-auditor/SKILL.md

@misc{s3-estate-calibration-auditor-2026,
  author    = {anyshift-io},
  title     = {S3 Estate Calibration Auditor [Claude Code skill]},
  year      = {2026},
  publisher = {ClaudSkills},
  url       = {https://claudskills.com/skills/s3-estate-calibration-auditor/}
}