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

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

Troubleshooting

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/