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/