Audit aws costs

Audit AWS Costs

Invocation: /audit-aws-costs in Claude Code; $audit-aws-costs in Codex.

Produce a clear, read-only picture of what exists in an AWS account, what it costs, and what was provisioned recently — so the user can decide what to keep, shut down, or delete. This skill never deletes or modifies anything by default. It gathers facts and presents an audit; teardown only happens later, on an explicit, per-resource request.

When to Use This Skill

This skill is invoked explicitly via /audit-aws-costs — it does not activate on its own. Run it when you want to answer questions like:

• "Audit my AWS costs" / "why is my AWS bill so high?"
• "What am I running in AWS?" / "What's provisioned in my account?"
• "Did I accidentally provision something with my credentials?"
• "Find idle / zombie / leftover AWS resources"
• "What can I safely shut down or delete?"

Safety Philosophy

This skill is strictly read-only:

• Every command is a describe, list, lookup, get, or Cost Explorer query. No create, run, delete, terminate, put, or modify.
• Never delete or stop anything as part of the audit, even if a resource looks obviously wasteful. Surface it; let the user decide.
• If the user asks to tear something down afterward, treat that as a separate action: confirm the exact resource, explain the blast radius, and only then act. Prefer deleting through the owning abstraction (CloudFormation / Terraform / CDK stack) over picking off individual resources.
• Report cost figures as what they are — actuals from Cost Explorer, not estimates — and label any back-of-envelope math clearly as an estimate.

Prerequisites

• AWS CLI v2 configured with working credentials (aws configure list).
• The audit reads from CloudTrail, Cost Explorer, and per-service describe APIs. Cost Explorer (ce:GetCostAndUsage) must be enabled on the account and the principal needs read access to it. If Cost Explorer is denied, skip that section and rely on the resource inventory plus a clearly-labelled estimate.

Environment Gotchas (read before running commands)

These bit a real run; bake them in:

• date: the user may have GNU coreutils on macOS, so BSD date -v-7d can fail. Prefer GNU syntax date -u -d '30 days ago' +%Y-%m-%dT%H:%M:%SZ. If that errors, fall back to BSD date -u -v-30d +%Y-%m-%dT%H:%M:%SZ.
• zsh reserved words: in zsh, status is read-only — never use it as a shell variable name in a loop. Use st or similar.
• Inline Python + AWS --query: avoid heredoc/inline Python with escaped quotes (the shell mangles \"). Write a small .py file (see scripts/cost-report.py) instead. Also avoid numeric comparisons inside JMESPath --query against cost amounts — the values arrive as strings and > comparisons error. Filter numbers in Python after the fact.
• CloudTrail is per-region and paged: lookup-events returns only the calling region's events, 50 per page. Sweep every enabled region, and let the AWS CLI walk every page — pass --page-size 50, not --max-results 50. The latter is the service-level cap, which disables the CLI's automatic pagination and silently truncates a busy region to a single 50-event page. scripts/sweep-regions.sh already uses --page-size.

Workflow

1. Identity and scope

Confirm who you are and where you're looking before reporting anything.

aws sts get-caller-identity
aws configure get region
# Enabled regions (excludes opted-out regions):
aws ec2 describe-regions --all-regions \
  --query 'Regions[?OptInStatus!=`not-opted-in`].RegionName' --output text

State the account ID and principal back to the user — an "accidental provisioning" worry is often really "which account/identity was I using?"

2. Recent provisioning — CloudTrail write-event sweep

CloudTrail is the authoritative log of every API call. Filter to write events (ReadOnly=false) over a 30-day window across all enabled regions. Use scripts/sweep-regions.sh, or inline:

bash scripts/sweep-regions.sh 30

Interpreting the output:

• Group by region and event name. Create*, Run*, Put*, Allocate* are provisioning. Note the Username column — was it the human IAM user, an assumed role, or an AWS service principal (a name ending in .amazonaws.com)?
• Service-driven write events with no matching human action usually mean an existing resource (a scaling group, a scheduled job, a deployment) is acting on its own — often a sign of a leftover that keeps retrying. Trace it to the resource that owns it rather than stopping at the event.
• To answer "did I provision this?", filter by the human user: --lookup-attributes AttributeKey=Username,AttributeValue=<iam-user>. If the only recent events for that user are read-only (Get*, Describe*, List*), they provisioned nothing recently — say so plainly.

3. Actual spend — Cost Explorer

Get real dollars by service, then by region, for the last two months:

# By service
aws ce get-cost-and-usage --region us-east-1 \
  --time-period Start=$(date -u -d '60 days ago' +%Y-%m-%d),End=$(date -u +%Y-%m-%d) \
  --granularity MONTHLY --metrics UnblendedCost \
  --group-by Type=DIMENSION,Key=SERVICE --output json \
  | python3 scripts/cost-report.py

# By region (re-run the python with the same JSON shape)
aws ce get-cost-and-usage --region us-east-1 \
  --time-period Start=$(date -u -d '60 days ago' +%Y-%m-%d),End=$(date -u +%Y-%m-%d) \
  --granularity MONTHLY --metrics UnblendedCost \
  --group-by Type=DIMENSION,Key=REGION --output json \
  | python3 scripts/cost-report.py

The service breakdown is the single most useful signal: it tells you whether the bill is storage, compute, data transfer, databases, or something else — which determines where to drill in step 5.

4. Billable-resource inventory

Enumerate the resource kinds that cost money even when idle, in each region that showed spend or recent activity (and your default region). For each, list id, state, size/type, and creation/launch time:

R=<region>
aws ec2 describe-instances --region $R \
  --query 'Reservations[].Instances[].{Id:InstanceId,Type:InstanceType,State:State.Name,Launched:LaunchTime}' --output table
aws ec2 describe-volumes --region $R \
  --query 'Volumes[].{Id:VolumeId,GiB:Size,State:State,Attached:Attachments[0].InstanceId}' --output table
aws ec2 describe-addresses --region $R \
  --query 'Addresses[].{IP:PublicIp,Associated:AssociationId}' --output table   # unassociated EIPs bill hourly
aws ec2 describe-nat-gateways --region $R \
  --query 'NatGateways[?State==`available`].NatGatewayId' --output table         # ~$32+/mo each
aws elbv2 describe-load-balancers --region $R --query 'LoadBalancers[].LoadBalancerName' --output table
aws elb   describe-load-balancers --region $R --query 'LoadBalancerDescriptions[].LoadBalancerName' --output table
aws rds   describe-db-instances --region $R \
  --query 'DBInstances[].{Id:DBInstanceIdentifier,Class:DBInstanceClass,Engine:Engine,Status:DBInstanceStatus}' --output table
aws autoscaling describe-auto-scaling-groups --region $R \
  --query 'AutoScalingGroups[].{Name:AutoScalingGroupName,Min:MinSize,Max:MaxSize,Desired:DesiredCapacity,Running:length(Instances)}' --output table
aws cloudformation describe-stacks --region $R \
  --query 'Stacks[].{Name:StackName,Status:StackStatus,Created:CreationTime}' --output table

See references/cost-drivers.md for the full cheat sheet of what bills while idle and the per-region vs. global services.

5. Drill into the top cost drivers

For whatever dominates step 3, get specifics. Examples:

• Storage-dominated bill → list buckets, their region, and sizes. Pull BucketSizeBytes from CloudWatch (free to query) with bash scripts/s3-sizes.sh. Flag the largest and newest buckets.
• Compute-dominated → which instances/ASGs are actually running vs. desired-but-failing. An ASG with Desired>0 but Running=0 is usually a zombie failing to launch; check aws autoscaling describe-scaling-activities for the failure reason.
• Database-dominated → RDS instance class, storage, and whether anything connects to it.

6. Produce the audit report

Synthesize everything into a single, skimmable report. Do not just dump command output. Lead with the verdict, then the evidence. Suggested shape:

## AWS audit — account <id> (<principal>), <date>

**Bottom line:** <1–2 sentences: total recent spend, top driver, and whether
anything was provisioned recently / unexpectedly.>

### 💸 What's costing money
| Resource | Region | Size/Type | ~Monthly | Created | Notes |
| ...sorted by cost, biggest first... |

### 🆕 Recently provisioned (last 30d)
| Resource | Region | By whom | When |
| ...from the CloudTrail sweep; empty is a valid, reassuring answer... |

### 🧟 Idle / zombie / leftover (low or zero cost, but cruft)
| Resource | Region | Why it looks abandoned |

### ✅ Suggested decisions (no action taken)
- Keep: ...
- Review: ...
- Candidate to shut down / delete: ... (and the single command the user could
  run, presented as a suggestion — not executed)

Rules for the report:

• Sort the cost table by dollars, descending. Money first.
• "Nothing was recently provisioned" / "no idle billable resources" are valuable, reassuring findings — state them explicitly rather than omitting.
• Distinguish costs money from just clutter. A leftover that bills $0 (e.g. an ASG whose launches all fail) is noise, not spend — say so.
• Every teardown is a suggestion the user can run, never something this skill performs. End by asking which, if any, they want help removing.

If the user then asks to remove something

Only on an explicit request, and one resource (or stack) at a time:

1. Show exactly what will be destroyed and its dependencies (aws cloudformation describe-stack-resources, or describe the resource).
2. Prefer deleting via the owning IaC stack so dependencies tear down in order.
3. Watch for orphans not managed by the stack (e.g. resources a deployment service spun up as copies) and for phantom references to already-deleted infrastructure — these can block a stack delete and may need --retain-resources on the failed resource after you confirm the underlying thing is truly gone.
4. Verify the end state with describe/list and report what remains.

These cleanup steps are out of scope for the audit itself — the audit stops at recommendations.