Five free AWS tools, one job each
Cost Explorer vs Compute Optimizer vs Trusted Advisor
AWS gives you five free cost tools with overlapping names and non-overlapping jobs. This is which one answers which question.
Cost Explorer answers "where did the money go". Compute Optimizer answers "what size should this be". Trusted Advisor answers "what is obviously wasted". Budgets answers "tell me before I overspend". The Pricing Calculator answers "what will this cost before I build it". Cost Anomaly Detection answers "did something change". They are not alternatives to each other, and using Cost Explorer to answer a rightsizing question is why people conclude the free tools are not enough.
One row each
| Tool | Question it answers | Data source | Cost |
|---|---|---|---|
| Cost Explorer | Where did the money go, by service, usage type, tag, region | Your billing data, up to 13 months | Free UI, $0.01 per API request |
| Compute Optimizer | What size should this instance, volume or function be | CloudWatch metrics over 14 days | Free |
| Trusted Advisor | What is obviously idle or unattached right now | Resource configuration plus utilisation | Cost checks need Business or Enterprise support |
| AWS Budgets | Alert me when spend passes a threshold or is forecast to | Billing data | First two budgets free, then $0.02 a day each |
| Cost Anomaly Detection | Did something change that I would not have predicted | Machine learning over your billing history | Free |
| Pricing Calculator | What will this cost before I build it | AWS list prices | Free |
| Cost and Usage Report | Everything, per resource, per hour | Raw billing records delivered to S3 | Free, plus S3 and query costs |
The confusions worth clearing up
- →Cost Explorer vs the Pricing Calculator. Cost Explorer is backward looking and shows what you spent. The Pricing Calculator is forward looking and estimates what a design would cost. They share almost nothing except the word cost.
- →Cost Explorer vs Cost and Usage Report. Cost Explorer is a friendly view with a 13-month window and no resource IDs. The Cost and Usage Report is the complete underlying record, per resource and per hour, delivered to S3 and queried with Athena. Everything Cost Explorer shows is derivable from the CUR; the reverse is not true.
- →Compute Optimizer vs Trusted Advisor. Trusted Advisor flags a low-utilisation instance. Compute Optimizer tells you which instance type to move it to and how confident it is. Compute Optimizer is free for everyone; Trusted Advisor’s cost checks are gated behind a support plan.
- →Budgets vs Cost Anomaly Detection. A budget fires when spend crosses a number you chose. Anomaly detection fires when spend deviates from the pattern it learned, even if the total is unremarkable. You want both, and both take under ten minutes.
- →Cost Optimization Hub vs all of the above. It aggregates recommendations from Compute Optimizer, Trusted Advisor, Savings Plans recommendations and others into one ranked list with estimated savings. Useful as a front door, and it introduces no data of its own.
The order to actually use them in
- 1Cost Explorer, six months, grouped by service. Establish where the money is before touching anything else. Then group the top service by usage type.
- 2Compute Optimizer, sorted by estimated saving. This is where the rightsizing decisions come from. Install the CloudWatch agent first if you can, because without memory metrics it under-recommends.
- 3Trusted Advisor, if your support plan includes it. The orphan list: idle load balancers, unassociated addresses, underutilised instances. Quick and unambiguous.
- 4Set a budget and turn on anomaly detection. Ten minutes, free, and the difference between finding the next problem in a week and finding it in a quarter.
- 5Enable the Cost and Usage Report even if you will not read it yet. It only starts collecting from the day you enable it, so enabling it early means the data exists when you eventually need per-resource detail.
Put numbers on it
Frequently asked questions
Is Cost Explorer free?
The console interface is free. The Cost Explorer API costs $0.01 per request, which is irrelevant for occasional use and adds up quickly for a tool polling it continuously. Enabling Cost Explorer for the first time takes about 24 hours to populate.
Is Compute Optimizer accurate?
For CPU and network bound workloads, yes, and the risk rating is conservative. Without memory metrics it systematically under-recommends, because it cannot tell a memory-bound instance from an idle one, so it plays safe. Installing the CloudWatch agent on your top instances materially improves it.
Do I need Business support for Trusted Advisor?
For the full cost optimisation checks, yes. Basic and Developer plans get a small subset. Everything Trusted Advisor would tell you about cost is available elsewhere for free, so this is not a reason to upgrade a support plan on its own.
Which one shows cost per resource?
Only the Cost and Usage Report, with resource IDs enabled. Cost Explorer aggregates and does not expose the individual instance or volume. If the question is "which specific volume is costing me this", the CUR queried through Athena is the only native answer.
Keep reading
Prices checked against AWS list rates on 2 August 2026. AWS changes prices; treat every figure here as a close approximation rather than a quote.
£499 fixed. Free scan first. 20%+ found or it’s free.
The scan is read-only — a role you create and delete, no keys shared — and shows your estimated monthly saving before anyone talks about money.