Billing and Cost Management

Overview

Analyze, optimize, and manage AWS costs. This skill encodes domain expertise from AWS's cost management products — gotchas, correct API usage patterns, and optimization workflows that models frequently get wrong.

Usage

Use this skill when:

Analyzing AWS spending, cost trends, or cost breakdowns
Setting up or managing budget alerts
Evaluating Savings Plans or Reserved Instance purchases
Right-sizing EC2, Lambda, RDS, or EBS resources
Looking up AWS service pricing
Running cost audits or investigating cost spikes
Querying CUR data with Athena
Scoping cost analysis to a specific billing view
Checking Free Tier usage

Core Concepts

Cost Explorer — query cost/usage data by service, account, tag, or time range
Budgets — set spending thresholds with alerts; supports billing view scoping
Billing Views — scope cost data to a subset of billing (custom view, billing group, or primary)
Compute Optimizer — right-sizing recommendations for EC2, Lambda, EBS, RDS
Cost Optimization Hub — aggregated savings recommendations across services
Savings Plans / Reserved Instances — commitment-based discounts
CUR 2.0 — detailed line-item billing data queryable via Athena

Recommended setup: Use the AWS MCP server for sandboxed execution, audit logging, and enterprise controls. See: https://docs.aws.amazon.com/aws-mcp/

Without AWS MCP: All commands use standard AWS CLI syntax and work with any agent that has CLI access.

Critical Rule: Always Check the Current Date

Before making ANY Cost Explorer, Budgets, or Savings Plans API call, you MUST determine the current date. Use a tool to get the current date and time — do NOT assume or guess the year. LLMs frequently default to dates from their training data instead of the actual current date, producing analyses of stale data that appear correct but are completely wrong.

Critical Rule: Deterministic Calculations

You MUST NEVER perform numerical calculations (sums, averages, percentages, comparisons, counts, min/max) by reasoning in your response. LLM arithmetic is unreliable and produces wrong answers on cost data.

You MUST ALWAYS use a script or calculator tool for any math on data returned from API calls. Write a Python script that performs the calculation and prints the result. If the AWS MCP server's run_script tool is available, use it. Otherwise, run the script locally.

Read references/deterministic-calculations.md for patterns and examples.

Decision Guide

Question	Tool	Reference
What am I spending? Where are costs going up?	Cost Explorer	`references/cost-explorer.md`
How much does a service cost?	Price List API	`references/pricing-lookup.md`
Where can I save money? (start here)	Cost Optimization Hub	`references/cost-optimization-hub.md`
Should I buy Savings Plans?	CE SP Recommendations	`references/savings-plans.md`
Should I buy Reserved Instances?	CE RI Recommendations	`references/reserved-instances.md`
Deep-dive on a specific EC2/Lambda/EBS/RDS rec?	Compute Optimizer	`references/ec2-rightsizing.md`, `references/lambda-optimization.md`, `references/rds-optimization.md`, `references/ebs-optimization.md`
How do I set up budget alerts?	Budgets	`references/budgets.md`
What's causing a cost spike?	Cost Anomaly Detection	`references/cost-explorer.md`
Am I within Free Tier?	Free Tier API	`references/free-tier.md`
How do I reduce my bill?	Cost Audit workflow	`references/cost-audit.md`
How do I query detailed billing data?	CUR 2.0 + Athena	`references/cur-athena.md`
How do I optimize specific services?	Per-service patterns	`references/service-optimization.md`
How do I scope costs to a billing view?	Billing Views	See Billing Views below

Common Tasks

Analyze costs by service

aws ce get-cost-and-usage \
  --time-period Start=2026-03-01,End=2026-04-01 \
  --granularity MONTHLY \
  --metrics UnblendedCost \
  --group-by Type=DIMENSION,Key=SERVICE

Default to UnblendedCost. Exclude Credits/Refunds with --filter '{"Not":{"Dimensions":{"Key":"RECORD_TYPE","Values":["Credit","Refund"]}}}'. End date is exclusive.

Run a cost audit

Read references/cost-audit.md for the full 7-step workflow: top cost drivers → month-over-month comparison → optimization recommendations → idle resources → commitment coverage → per-service quick wins → report.

Get right-sizing recommendations

Compute Optimizer requires opt-in first: aws compute-optimizer update-enrollment-status --status Active. Then read references/ec2-rightsizing.md for EC2 or the relevant resource-specific reference.

Look up service pricing

Read references/pricing-lookup.md for service codes and attribute filters. Common trap: Price List API service codes differ from Cost Explorer service names.

Billing Views

A billing view scopes cost and usage data to a specific slice of an account's billing (e.g., a billing group, custom view, or the default primary view). When the user wants to analyze costs through a particular billing view, add --billing-view-arn to supported API calls.

Discover available billing views

aws billing list-billing-views \
  --billing-view-types PRIMARY CUSTOM BILLING_GROUP

Requires billing:ListBillingViews permission.

Use a billing view with Cost Explorer

aws ce get-cost-and-usage \
  --time-period Start=2026-03-01,End=2026-04-01 \
  --granularity MONTHLY \
  --metrics UnblendedCost \
  --group-by Type=DIMENSION,Key=SERVICE \
  --billing-view-arn arn:aws:billing::ACCOUNT_ID:billingview/BILLING_VIEW_ID

Create a budget scoped to a billing view

In the --budget JSON, include the BillingViewArn field:

aws budgets create-budget --account-id ACCOUNT_ID \
  --budget '{
    "BudgetName": "TeamX-Monthly",
    "BudgetLimit": {"Amount": "1000", "Unit": "USD"},
    "TimeUnit": "MONTHLY",
    "BudgetType": "COST",
    "BillingViewArn": "arn:aws:billing::ACCOUNT_ID:billingview/BILLING_VIEW_ID"
  }'

API support for `--billing-view-arn`

Supports `--billing-view-arn`	Does NOT support it
`ce get-cost-and-usage`	`ce get-reservation-coverage`
`ce get-cost-and-usage-with-resources`	`ce get-reservation-utilization`
`ce get-cost-forecast`	`ce get-savings-plans-coverage`
`ce get-usage-forecast`	`ce get-savings-plans-utilization`
`ce get-dimension-values`
`ce get-tags`
`ce get-cost-comparison-drivers`
`budgets create-budget` (in budget JSON)

Troubleshooting

Error	Cause	Fix
`ValidationException` on Cost Explorer	Wrong dimension key (e.g., `CHARGE_TYPE` instead of `RECORD_TYPE`)	Use `RECORD_TYPE` for charge type filtering
Empty results with filter	Filter value doesn't match exactly	Call `GetDimensionValues` first to get valid values
`AccessDeniedException` on hourly data	Hourly granularity not enabled	Enable in Cost Explorer preferences
`Account not registered` on Compute Optimizer	Not opted in	Run `update-enrollment-status --status Active`
Budgets API fails outside us-east-1	Budgets requires us-east-1	Set `--region us-east-1`
Cost Explorer `Total` empty with GroupBy	By design — totals excluded when grouping	Make separate call without GroupBy, or sum grouped results using a script
`AccessDeniedException` on `list-billing-views`	Missing permission	User needs `billing:ListBillingViews` permissions
`ValidationException` with `--billing-view-arn`	API doesn't support billing views, or malformed ARN	Check the API support table above; ARN format is `arn:aws:billing::ACCOUNT_ID:billingview/VIEW_ID`
Budget shows `UNHEALTHY` health status	Billing view access revoked or view deleted	Check `HealthStatus.StatusReason` in `describe-budget` output; ensure `billing:GetBillingViewData` is granted

Additional Resources

AWS Cost Management User Guide: https://docs.aws.amazon.com/cost-management/
AWS Pricing Calculator: https://calculator.aws/
Compute Optimizer User Guide: https://docs.aws.amazon.com/compute-optimizer/
Well-Architected Cost Optimization Pillar: https://docs.aws.amazon.com/wellarchitected/latest/cost-optimization-pillar/

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